Revision of Tympanopleura Eigenmann ( Siluriformes : Auchenipteridae ) with description of two new species

The Neotropical catfish genus Tympanopleura, previously synonymized within Ageneiosus, is revalidated and included species are reviewed. Six species are recognized, two of which are described as new. Tympanopleura is distinguished from Ageneiosus by having an enlarged gas bladder not strongly encapsulated in bone; a prominent pseudotympanum consisting of an area on the side of the body devoid of epaxial musculature where the gas bladder contacts the internal coelomic wall; short, blunt head without greatly elongated jaws; and smaller adult body size. Species of Tympanopleura are distinguished from each other on the basis of unique meristic, morphometric, and pigmentation differences. Ageneiosus melanopogon and Tympanopleura nigricollis are junior synonyms of Tympanopleura atronasus. Tympanopleura alta is a junior synonym of Tympanopleura brevis. A lectotype is designated for T. brevis. Ageneiosus madeirensis is a junior synonym of Tympanopleura rondoni. Tympanopleura atronasus, T. brevis, T. longipinna, and T. rondoni are relatively widespread in the middle and upper Amazon River basin. Tympanopleura cryptica is described from relatively few specimens collected in the upper portion of the Amazon River basin in Peru and the middle portion of that basin in Brazil. Tympanopleura piperata is distributed in the upper and middle Amazon River basin, as well as in the Essequibo River drainage of Guyana.


Introduction
The Auchenipteridae, commonly known as driftwood catfishes, is a monophyletic group that currently includes approximately 113 valid species in 23 genera and two subfamilies, the Auchenipterinae and Centromochlinae (Ferraris, 2003(Ferraris, , 2007;;Eschmeyer & Fong, 2015).The family is endemic to the Neotropics and widely distributed throughout South America and lower Central America.Species of the family are small-to medium-sized, generally secretive and nocturnal in their habits, and are unique in their reproductive biology among doradoid catfishes by having internal insemination (Ferraris, 2003).In recent years a number of revisionary and phylogenetic studies have greatly improved knowledge about the taxonomy and relationships of species and genera in this group, whereas unresolved problems and additional studies and discoveries are expected to add significantly to the number of recognized taxa in the future (Ferraris, 2003).
The genus Tympanopleura was proposed by Eigenmann (1912) for a single species of auchenipterid catfish, T. piperata, described from eight specimens collected in the Essequibo River, Guyana.Eigenmann (1912) recognized T. piperata as distinct from species of Ageneiosus Lacepède, 1803, on the basis of an enlarged gas bladder projecting laterally to the sides of the coelomic cavity, devoid of overlying musculature and with a thin external cutaneous covering, forming a "pseudo-tympanum".Subsequently, Eigenmann & Myers in Myers (1928) described T. alta from the río Marañon, Peru, and Eigenmann & Allen (1942) described T. nigricollis from the Iquitos region of Peru, stating that the species was "related to T. polystictus (Steindachner, 1915) and T. rondoni (Miranda Ribeiro, 1914)", the later two species of which were originally described in Ageneiosus.In addition to the aforementioned taxa, some species described prior to or after Eigenmann's (1912) designation of Tympanopleura were subsequently considered by various authors (e.g., Britski, 1972;Ferraris, 1988;Walsh, 1990) to be related on the basis of the enlarged gas bladder and other morphological similarities.These species include Ageneiosus brevis Steindachner, 1881, Ageneiosus atronasus Eigenmann &Eigenmann, 1888, andAgeneiosus rondoni Miranda Ribeiro, 1914.A few other nominal species described in Ageneiosus were treated by recent investigators as junior synonyms of the species listed above, but taxonomy of the group has remained problematic.
For many years nominal species of Tympanopleura and Ageneiosus were treated together in a single family, the Ageneiosidae, and their putative relationship was recognized within a larger clade of catfishes, primarily on the basis of derived morphological modifications of the Weberian complex and presence of an elastic spring apparatus used for sound production (Fine & Ladich, 2003).Ferraris (1988) hypothesized that species previously recognized in the Ageneiosidae were most closely related to species of Trachelyopterus Valenciennes, Trachelyichthys Mees, and an Auchenipterus-group (=Auchenipterus Valenciennes + Entomocorus Eigenmann + Epapterus Cope), all of which he included in an "Auchenipterini" tribe.He also expanded the Auchenipteridae to include the species previously grouped in the Ageneiosidae.

Material and Methods
Meristic and morphometric data were collected from whole specimens deposited at the institutions listed below.Rays of paired and unpaired fins were counted by examining specimens under a stereomicroscope with the aid of substage transmitted light, from radiographs, and in a few cases from cleared-and-stained specimens.Clearing and staining methods followed the procedure of Potthoff (1984) and Taylor & van Dyke (1985), and these specimens are indicated as "c/s" in material examined; skeletonized specimens are indicated as "skel".Dissection and photography of gas bladders followed the methods of Birindelli et al. (2009Birindelli et al. ( , 2012)).Nomenclature of osteology and other morphological features follows Cailliet et al. (1986), Arratia (2003a,b) and Chardon et al. (2003).Fin-ray counts included all lepidotrichia; for the dorsal and anal fins, counts included two rays that articulate on the last distal pterygiophore.Rudimentary fin rays occur irregularly on the anterior-most distal pterygiophore of the anal fin.Such rudimentary elements were included in anal-fin ray counts if they appeared to articulate with the first distal pterygiophore or extended into the membranous portion of 3 the fin sufficiently to be visible under magnification.In cases where an anterior rudimentary element was visible only as a small "floating" splint in a radiograph it was not included in the anal-fin ray count.Pectoral-fin rays were preferentially counted on the left side, but occasionally on the right side when the left was damaged or distorted.No effort was made to discern unbranched from branched rays except in the case of the pelvic fin (always with one unbranched and six branched), the caudal fin, where counts are reported for principal rays (one unbranched and all branched rays each for the dorsal and ventral lobes) and the upper and lower procurrent rays, and for the anal fin in delimiting rays associated with the intromittent organ of nuptial males.Vertebral counts were made from radiographs and clearedand-stained specimens, and the total number included six for the Weberian apparatus, and one for the fused preural and ural (PU1+U1) centra following the terminology of Lundberg & Baskin (1969).Preanal vertebrae were defined as those with hemal spines anterior to the first proximal anal pterygiophore.Number of pleural rib pairs was determined from radiographs or from cleared-and-stained specimens.Gill raker counts, taken from either side but preferentially on the left, were those of the lateral row on the first branchial arch and recorded as upper, lower, and total.Any gill raker at the articulation between epibranchial and ceratobranchial was included with the upper count.Mean counts of meristic characters among species were tested for significant differences using analysis of variance (Kruskal-Wallis ANOVA and Tamhane's T2 posthoc individual comparison between species with unequal variances; p ≤ 0.01), with PASW Statistics Base Version 17.0 (IBM SPSS, 2009).
A combination of 31 truss and conventional measurements were taken to evaluate differences in body shape among species.Measurements involving bilateral landmarks were preferentially made on the left side of the body.Morphometric data were taken as straight-line, pointto-point measurements with needlepoint dial calipers, or, in the case of small specimens (e.g., T. piperata), using an ocular micrometer fitted to a stereomicroscope.Measurements were recorded to the nearest 0.1 mm and are summarized in species accounts and tables as percentages of Standard Length (SL) or Head Length (HL), the latter measured as the distance from the tip of the snout to the upper apex of the opercular opening.Distances between fins were measured from landmarks using the terms "origin" and "insertion" to indicate the anterior and posterior points of contact between fin rays and the body, respectively (Cailliet et al., 1986).The limits of most measurements are self-evident from the descriptors.Select measurements are delimited as follows: caudal peduncle length was measured from the anal-fin insertion to the base of the hypural plate; head depth was the vertical distance between the center of the supraoccipital and the isthmus; dorsal interopercular width was the distance between the dorsal apex of the opercular openings; anterior internarial width was the distance between the anterior narial openings; snout length was measured from the median tip of the upper jaw to the front margin of the eye; preisthmus length was the distance from the median tip of the upper jaw to the midpoint between where the branchiostegal membranes attach to the symphysis; eye diameter was the horizontal length of the eyeball excluding any fleshy tissue overlying the orbit.
To evaluate shape differences among species, the covariance matrix of log-transformed measurements was analyzed using sheared principal component analysis (PCA) [Bookstein et al. (1985) and a modified, unpublished algorithm by D.L. Swofford] with SAS Version 9.1 Software (SAS Institute, 2008).Scores on the second and third sheared principal components, which represent size-free shape factors, were plotted for individual specimens to examine multivariate differences among species.Dorsal-fin length and maxillary barbel length were omitted from multivariate analyses due to sexual dimorphism of these structures in nuptial adults.Morphometric data from primary types of each species were included in PCA computations.Variation in meristic and morphometric data of material examined are reported as means (mean ± one standard seviation (SD)).
The base distribution map used to plot species records was modified from HydroSHEDS geospatial data compiled and developed by the Conservation Science Program of the World Wildlife Fund (http://hydrosheds.cr.usgs.gov/index.php).Citations listed under synonyms in each species account are not purported to be exhaustive.Rather, citations are intended to provide the reader with the most relevant published and unpublished literature about this relatively poorly studied group of fishes.
Institutional abbreviations are: AMNH, American  Ferraris, 1988): lateral line sinusoidal and forked at the base of the caudal fin; urogenital pore of reproductively active adult males located at the distal tip of the anterior margin of the anal fin; urogenital pore of reproductively active adult females enlarged; and sexually dimorphic dorsal-fin spine.In the Auchenipterinae, Tympanopleura, Ageneiosus, Tetranematichthys, Entomocorus, Auchenipterus, Epapterus, and Pseudepapterus are distinct by the ventrolaterally positioned eyes visible in both dorsal and ventral views.Compared to species of Ageneiosus, the species of Tympanopleura have a more gently rounded anterior profile of the head (Fig. 1) and less protruded upper jaw, reflected by a shorter relative preorbital distance and distinctive differences in osteology associated with the jaws and cranium as detailed below.Tympanopleura, Ageneiosus, and Tetranematichthys share the following unique combination of characters in the Auchenipterinae: anterior fork of the mesethmoid directed anterolaterally, at an approximate angle of 45° relative to the anterior border of the bone (except in Ageneiosus inermis and A. polystictus); nasal bifurcated with an ossified accessory lateral tube directed anteriorly; vomer rounded anteriorly, without lateral projections (also in a number of unrelated siluriforms); snout elongate, greater than horizontal eye diameter (except in T. piperata); premaxilla variably developed posterolaterally, more elongated in species of Ageneiosus, less so in species of Tympanopleura and Tetranematichthys, where the posterior projection of the premaxilla does not reach past a plane passing through the posterior margin of the autopalatine; laminar expansion of bone on posteromedial margin of premaxilla; reduced number of teeth on posterior extremity of premaxilla; maxillary barbel very short; mandibular barbels absent in adults (Ageneiosus and Tympanopleura), or one pair present (Tetranematichthys; also in Gelanoglanis Böhlke); tooth-bearing surface of dentary expanded near symphysis, with variable number of tooth rows (greatest in Ageneiosus, reduced in Tympanopleura); reduction in number of bones in infraorbital series to four (also in Liosomadoras Fowler and Asterophysus Kner within the Auchenipteridae, in most doradids, and in a number of unrelated siluriforms); first infraorbital (lacrimal) bifurcated anteriorly; first infraorbital separated from neurocranium; second infraorbital flared posteriorly, funnel or trumpet shaped (tubular in Tetranematichthys); posterior infraorbital canal ossification separated from sphenotic, with an unossified section of the infraorbital sensory canal; parurohyal with medial projection directed dorsally and articulating with or extending between hypohyals (also in Tocantinsia Mees); osseus expansion on dorsal region of parurohyal weakly developed; anterior ceratohyal sutured to ventral hypohyal along ventromedial surface (also in Oxydoras Kner); anteriomedial tips of first two hypobranchials concave and obliquely angled anteriomedially; medial tip of first epibranchial larger than that of second, usually covering the latter element dorsally (except T. piperata); quadrate with enlarged dorsomedial lamina separating articular surfaces of hyomandibula and metapterygoid; bones of cephalic shield trabeculate; anterior nuchal plate absent [also in Epapterus, Pseudepapterus within the Auchenipteridae; but see Ferraris (1988)]; long anterolateral process on sphenotic (also in some doradids and unrelated African taxa); epioccipital bifurcated distally, with a posterior laminar extension, broadly sutured with expanded parapophyses of fifth and sixth vertebrae, median branch of posterior process larger than lateral branch (also in Pseudepapterus, Trachelyichthys, and Trachelyopterus); seventh vertebra not sutured to complex centrum (also in Pseudepapterus, Wertheimeria Steindachner within the Auchenipteridae), or in contact with an expansion of the ventral margin (Tetranematichthys); posterior process of coracoid absent or rudimentary (also in Diplomystes Bleeker); third pectoral-fin pterygiophore expanded distally and supporting several rays; postcleithral process absent, rudimentary, or only weakly developed (also in Pseudepapterus within the Auchenipteridae); anterior margin of dorsal-fin spine of nuptial males armed with antrorse serrae of varying configuration; 2-4 pairs of dorsal-fin inclinator muscles (also in Pseudepapterus and Trachelyopterus within the Auchenipteridae, versus 1 pair in other doradoids and unrelated taxa).Most of the derived features of the neurocranium as listed above are illustrated in Figs.2-4.Tympanopleura and Ageneiosus are distinct from all other auchenipterids in lacking mandibular barbels as adults (but see Remarks), and, except for nuptial males, in having the maxillary barbels greatly reduced in size, filiform, and lying in a groove at the corner of the mouth above the upper lip.In nuptial males of species in these two genera, the maxillary barbel has an inner ossified core and is armed with sharp, recurved bony hooks on the anterodorsal and posterodorsal margins.Additionally, nuptial males of Tympanopleura and Ageneiosus have an elongated, sinusoidal or nearly straight dorsal-fin spine that can be hyperabducted anteriorly, and that is ornamented with prominent, sharp antrorse serrae on the anterior margin; these characters are shared to different degrees of development among genera and species in the Auchenipterini as proposed by Ferraris (1988), which includes Tympanopleura, Ageneiosus, Tetranematichthys, an Auchenipterus-group, Trachelyopterus, and Trachelyichthys.
Tympanopleura differs from Ageneiosus in having a smaller adult body size, a large cordiform gas bladder that is unencapsulated in bone, a prominent pseudotympanum, or hiatus of musculature where the gas bladder contacts the lateral body wall (Fig. 5) that is readily visible externally, and parapophyses of the fourth vertebrae (=Müllerian rami) consisting of large, discoidal plates closely adpressed to windows on the anterodorsal face of the anterior chamber of the the gas bladder.Tympanopleura, with the exception of T. piperata, also differs from Ageneiosus in having paired posterior diverticula on the gas bladder (but see Remarks).
In addition to the features described above that also distinguish Tympanopleura from Ageneiosus, Tympanopleura is further distinguished from Tetranematichthys by the absence of a single pair of mandibular barbels with serrated margins or multiple fleshy, digitiform processes at their distal tips (Vari & Ferraris, 2006;Peixoto & Wosiacki, 2010).Additionally, nuptial male Tetranematichthys lack the characteristic sharp recurved bony hooks on the maxillary barbel present in Tympanopleura and Ageneiosus, and the swimbladder in Tetranematichthys has a large anterior chamber with posterior diverticula enlarged and fused, unlike the structure in Tympanopleura (Birindelli et al., 2012).
Description.Tympanopleura comprises species of small to medium sized auchenipterids, ranging in maximum size from about 50 mm SL (T.piperata) to 160 mm SL (T.rondoni).Body widest at pectoral-fin origin, moderately to strongly compressed posteriorly.Dorsal and ventral aspects of body gently tapered posteriorly, greatest body depth at base of dorsal fin.Head moderately depressed, dorsal profile gently sloping upward to anterior margin of supraoccipital, inflected more acutely to dorsal-fin origin.Mouth inferior to nearly terminal (T.piperata).Eye size variable between species but relatively large (8-36% HL), displaced laterally and visible in both dorsal and ventral views, lacking circumorbital sulcus, covered with thick epidermis continuous with that on side of head.Large opercular opening, gill membranes broadly fused to isthmus.Premaxilla and dentary with relatively few irregular rows of small, unicuspid teeth; premaxilla not greatly expanded anteromedially.Salient aspects of head osteology as listed under Diagnosis.
Single pair of maxillary barbels, diminutive, filiform and fleshy for most of length in all but nuptial males, lying in small groove above upper lip.Maxillary barbel of nuptial male elongated, ossified entire length; at peak development with sharp, antrorse, tooth-like hooks on dorsomedial and ventromedial surfaces.Mandibular barbels absent in adults; small juveniles occasionally with 1-2 pair of minute chin barbels that become resorbed with growth.
Lateral-line canal extending from dorsomedial margin of posttemporal midlaterally along trunk to base of caudal fin, sinusoidal, with several short dorsal and ventral rami obliquely directed posteriorly, each branch passing to the surface and ending in a small pore.Lateral-line bifurcated at base of caudal fin with a short, branched ramus extending posteriorly a short distance on each fin lobe.
Suspensorium large but not greatly elongated and oriented in moderately oblique dorso-ventral plane.Quadrate with dorsomedial lamina extending between and broadly sutured to hyomandibular and metapterygoid, the latter bone laminar, roughly quadrangular, articulating synchondrally with quadrate near posteroventral corner.Hyomandibular articulates synchondrally with sphenotic by short anterodorsal process.Suprapreopercle small, rod-like, investing short section of preopercular latero-sensory canal anteroventral to exit from pterotic.Preopercle moderately large blade, smooth on all margins, sutured anteroventrally with quadrate.Preopercular latero-sensory canal with posterior and ventral branches exiting at anteroventral corner.Small bone, presumed mesopterygoid (but see Walsh, 1990) anterior to metapterygoid, superficially contacting vomer anteromedially, medial to palatine.
Hyoid arch consisting of unpaired urohyal, and paired hypohyal, ceratohyal, interhyal, epihyal, and branchiostegal bones.Urohyal broadly rounded anteriorly, with long, laminar projection posteriorly and a vertical extension between hypohyals anteromedially.Ceratohyal sutured anteriorly to ventral ossification of the hypohyal along its ventromedial surface; posteriorly, ceratohyal articulated suturally and synchondrally with interhyal.Total of 7-10 branchiostegal rays, first 6-7 supported by ceratohyal, remaining ones supported by interhyals.Second and third basibranchials ossified.First two hypobranchials ossified, obliquely concave on anterior margin, with medial cartilaginous flange anterior to lateral edge.Five ossified epibranchials and ceratobranchials; posterior ceratobranchial pair expanded posteromedially and supporting large pharyngeal tooth plates, each with short, conical teeth.Relatively large gill rakers on medial and lateral margins of epibranchials and ceratobranchials, numbering 4-10 on epibranchial, 9-24 on ceratobranchial.Pair of relatively large oval pharyngeal tooth plates supported by infrapharyngobranchials and posterior tips of ossified third and fourth epibranchials.Anteromedial tip of first epibranchial broadly flared and overlapping medial tip of second epibranchial.
Complex centrum formed by first six vertebrae, combined with modifications of posterior neurocranium and supporting elements of dorsal fin to form Weberian apparatus, the entire complex modified to form an elastic spring apparatus.Müllerian ramus large, discoidal, apposed anterodorsally to gas bladder tunica.Gas bladder enlarged, unencapsulated in bone, cordiform or longitudinally elongated, with a pair of short posterior terminal diverticula (except T. piperata).Large pseudotympanum formed by hiatus of epaxial musculature and lateral contact of gas bladder with body wall.
Dorsal fin with single small spinelet, large spine, six thin branched rays, five proximal pterygiophores, entire base of fin short.Dorsal spine pungent, typically with crenulate anterior margin and series of small, sharp or conical retrorse serrae on posterior margin in juveniles, females, and nonbreeding males.Nuptial males with highly modified dorsalfin spine, lengthened and thickened, anterior margin with sharp, antrorse serrae, typically in two rows basally, single row distally, aligned along or oblique to midsagittal plane; rear margin of spine smooth.Adipose fin small, posterior margin forming a free flap.
Cleithrum broadly fused to coracoid along entire anteroventral margin; coracoids broadly sutured at midline.Postcleithral process absent or reduced to a small conical projection.Pectoral fin with single pungent spine and 6-13 branched rays supported by three ossified radials, the last radial expanded posteriorly and supporting multiple rays.Anterior margin of pectoral-fin spine weakly to moderately crenulate or rugose, dorsal and ventral margins with shallow grooves to nearly smooth, posterior margin with 12-37 retrorse serrae extending along entire shaft, usually in single row, occasionally bifurcated or split into two rows proximally.Posterior margin of fin straight or slightly falcate, anterior rays longest.
Pelvic fin abdominal, with single unbranched and 6 branched rays, unbranched ray thickened.First branched ray longest, medial rays progressively shorter, distal margin of fin straight to slightly rounded.
Anal fin long, 23-42 rays.First pterygiophore typically with a small ray-like splint of bone anteriorly (occasionally two), and a single well-developed unbranched ray.Last pterygiophore with slightly expanded dorsal lamina and supporting two short-branched rays.Distal margin of fin straight to slightly convex; anterior rays longest, progressively shorter posteriorly.Anal fin sexually dimorphic; in prenuptial and nuptial males the fin forms an intromittent organ, with the first 5-6 rays thickened and elongated, and progressive development of a tube-like canal anteriorly and displacement of the urogenital pore to near the distal tip of the first fin ray.
Pigmentation on head, body, and fins relatively drab, consisting of nearly uniform brown to gray countershading and light to unpigmented areas on venter (T.brevis, T. cryptica, T. longipinna), or with distinctive pattern consisting of prominent large blotches, irregular spots, or stippling (T.atronasus, T. piperata, and T. rondoni).

Remarks on the distinction between Tympanopleura and
Ageneiosus.Although Tympanopleura and Ageneiosus are distinguished from all other auchenipterids in lacking mandibular barbels, this character state requires qualification in that it applies only to adult specimens, a condition that has not been cited in the literature.Walsh (1990) found one to two pairs of minute barbels on the chins of several juvenile specimens of two species of Tympanopleura and at least three species of Ageneiosus; barbels were described as short, fleshy, and apparently derived from superficial integument.We did not exhaustively examine all specimens used in this study for this character, but we were able to confirm the presence of chin barbels in at least a dozen specimens of T. atronasus as well as some specimens of T. piperata.Walsh (1990) described an apparent heterochronic process whereby mandibular barbels may appear early in development and are resorbed with growth, similar to a situation in some species of Pangasiidae (Karamchandani & Motwani, 1956;Fumihito, 1989).As noted by Fox (1999), the lability of barbels in siluriforms and cypriniforms necessitates that caution be exercised when making comparisons between taxa, and that phylogenetic inferences on the basis of presence or absence of barbels, their structure, number, and location may be of value, but within a framework of additional corroborative morphological characters.There is a general lack of information regarding structure and function of mandibular barbels in siluriforms (Diogo & Chardon, 2000), and a study of their embryological development and ontogenetic fate in Tympanopleura and Ageneiosus could be informative.
Species of Tympanopleura exhibit variation in the presence of a postcleithral process on the pectoral girdle.A small or rudimentary postcleithral process is typically present in T. brevis, T. cryptica, T. piperata, and T. rondoni.The postcleithral process appears to be uniformly absent in other species of Tympanopleura and in all species of Ageneiosus.The primitive condition for catfishes in general is the presence of a moderately developed, unornamented postcleithral process.However, there is considerable variation among siluriforms in size and ornamentation of the postcleithral process, and the structure has been independently reduced or lost in several lineages (Stewart, 1986).At the opposite extreme from Tympanopleura and Ageneiosus, most other auchenipterids have a well-developed postcleithral process, and in doradids it is generally prominent and in many species conspicuously ornamented with grooves and ridges (among auchenipterids, the postcleithral process is also reduced in Tetranematichthys and Pseudepapterus hasemani).Stewart (1986) noted a positive correlation between relative size of the postcleithral process and strength of the pectoral-fin spine and locking mechanism in pimelodids.
A similar condition appears to exist in doradoids, and within Tympanopleura, those species with the most robust pectoral-fin spines (T.brevis and T. rondoni) have the most prominent postcleithral process, whereas the other species with weak pectoral-fin spines have the process reduced (rudimentary in T. cryptica and T. piperata) or absent altogether.Moreover, we noted considerable variation among species of Tympanopleura in which the postcleithral process is present; in some cases specimens either exhibited or lacked the postcleithral process (even within a single lot), and occasional individuals were observed to have the process variably developed bilaterally.
The unique structure of the doradoid gas bladder has long been of keen interest from a taxonomic, anatomical, and functional perspective (e.g., Bridge & Haddon, 1889, 1892, 1893;Eigenmann, 1925;Chardon, 1968;Birindelli et al., 2009Birindelli et al., , 2012)).Early authors considered a gas bladder greatly reduced in size and encapsulated in a bony capsule associated with the complex centrum and Weberian apparatus to be a diagnostic feature of Ageneiosus.In the original description of Ageneiosus (=Tetranematichthys) quadrifilis, Kner (1858) illustrated the unusal globular, bipartite gas bladder of this species, which may have subsequently led to some confusion about its taxonomic relationship relative to species that were considered at the time as congeners.The taxonomic scope of an Ageneiosus group and the known morphological variation of the gas bladder by species represented therein was expanded when Eigenmann (1912) described the genus Tympanopleura, for the type species T. piperata, based on the salient feature of the "air bladder projecting into the abdominal cavity, naked laterally, the skin over it forming a large pseudotympanum".This was further elaborated by Eigenmann & Myers (in Myers, 1928) and by Eigenmann & Allen (1942) with subsequent descriptions of the nominal species T. alta and T. nigricollis.
In a detailed comparative analysis of gas bladder morphology among auchenipterid genera, Birindelli et al. (2012) found a suite of characters of value for inference of phylogenetic relationships within the family.Most species of auchenipterids have relatively simple gas bladders, characterized as cordiform with smooth walls, internal T-shaped septa, and with the modified and expanded parapophyses of the fourth vertebrae (Müllerian rami) attached to the anterodorsal margins of the gas bladder.Together the Müllerian rami and protractor muscles form an elastic spring apparatus, a synapomorphy shared by auchenipterids and doradids (and also present in mochokids, ariids, malapterurids, and pangasiids), that is used in sound production (Fine & Ladich, 2003;Kaatz & Stewart, 2012).In their study, Birindelli et al. (2012) proposed eight characters and alternate states of each to construct a hypothesized phylogeny of the Auchenipteridae.Therein, the authors proposed an Ageneiosus group characterized by the shared presence of a gas bladder with posterior, short, thin terminal diverticula.Within their Ageneiosus group, the authors proposed two independent lineages, one consisting of species with a reduced, diminutive gas bladder and pseudotympanum, and a lineage with an unreduced gas bladder and large pseudotympanum, comprised of A. atronasus, A. brevis, and A. piperatus (herein placed in Tympanopleura).Recognition of distinct clades represented by species with an enlarged gas bladder and pseudotympanum versus those with reduced, variably ossified gas bladders was independently corroborated by Ribeiro (2011), in combination with other characters supporting a presumably monophyletic Tympanopleura lineage.
Given the prevailing evidence provided by recent and historic investigations, we formally recognize Tympanopleura as a valid genus and restrict Ageneiosus to related species that share a reduced gas bladder and pseudotympanum, and larger maximum adult body size.Nonetheless, considerable variation exists in gas bladder morphology, especially concerning its relative size, the ossification process (where present), and development (or secondary loss) of diverticula, such that much remains to be explored.Britski (1972) and Walsh (1990) found evidence of allometric and ontogenetic changes in size and degree of ossification in some species, and there appear to be possible homoplasies in gas bladder morphology among some species of Ageneiosus and Tympanopleura.Ageneiosus pardalis, a trans-Andean species, retains a large gas bladder, and A. militaris and A. magoi have only a partially reduced gas bladder, yet these species are postulated to be related to those taxa with greatly reduced, encapsulated gas bladders (Britski, 1972;Walsh, 1990;Ribeiro, 2011).Conversely, T. piperata, with a large gas bladder lacking diverticula, exhibits partial ossification of the tunica externa and internal longitudinal septum in adults.In summary, species of Tympanopleura are diagnosed by the shared condition of a prominent pseudotympanum (Fig. 5) and a large, cordiform or slightly elongate gas bladder (Fig. 6).In contrast, most species of Ageneiosus have, as adults, a greatly reduced gas bladder that is partially to fully encased in bone as a result of progressive ossification involving the complex centrum, and, possibly, ossification of the tunica itself (Fig. 7).

Morphometrics. A principal component analysis (PCA)
of Tympanopleura species resulted in complete separation of T. longipinna and T. piperata along sheared principal component III (PC3) from a combination of T. atronasus, T. brevis, T. cryptica, and T. rondoni (Fig. 8a).The latter four species were generally separated from each other along sheared principal component II (PC2) with marginal overlap among groupings of two species each.In the multispecies comparison variable loadings on the first principal component were positive and indicative of principal component I (PC1) as a general size factor (Bookstein et al., 1985).PC1 accounted for 93.0% of the total variance in the complete covariance matrix, with sheared PC2 and sheared PC3 accounting for 3.0% and 1.6%, respectively, thus totaling 97.6% for the first three principal components (Table 7).Variables that loaded most heavily with positive values along sheared PC2 were: eye diameter (0.36), caudal peduncle depth (0.31), caudal peduncle length (0.29), and pelvic-fin origin to adipose-fin origin (0.20).Variables that loaded most heavily with negative values along sheared PC2 were anterior internarial distance (-0.31), snout length (-0.29), upper jaw length (-0.25), and gape width (-0.23).
Along sheared PC3, heaviest positive loadings were for anal-fin base length (0.45), pelvic-fin origin to adipose-fin origin (0.33), and dorsal-fin origin to adipose-fin origin (0.22); greatest negative loading along this axis was for eye diameter (-0.63).Not unexpectedly and corresponding to their greater anal-fin ray counts, T. longipinna and T. piperata stand apart from the other species in having relatively longer anal-fin base lengths; likewise, rank order of mean values of this measurement for the other species trended with the anal-fin ray counts of each species.As a proportion of SL, T. longipinna and T. piperata have greater distances from the pelvic-fin origin to dorsal-fin origin, and the dorsal-fin origin to adipose-fin origin in comparison to the other species.Relative to head length, T. piperata has the largest eye size, whereas T. rondoni has the smallest.In order to evaluate shape differences between T. atronasus, T. brevis, T. cryptica, and T. rondoni, additional principal component analyses were made between combinations of two species each, with the exceptions of T. atronasus and T. brevis, T. atronasus and T. rondoni, and T. cryptica and T. rondoni, each combination of which showed no overlap in the plot of principal component scores in the multi-species comparison.In each dualspecies comparison, plots of principal component scores resulted in complete separation along the sheared PC2 axis (Figs.8b-d).
In the PCA between T. atronasus and T. cryptica (Fig. 8b), PC1 accounted for 92.8% of the variance for the total covariance matrix, with 96.6% of the cumulative variance attributed to the first three principal components.
Measurements with greatest positive loadings along sheared PC2 were body depth at dorsal-fin origin (0.42), pectoral spine length (0.29), adipose-fin origin to anal-fin insertion (0.25), and pectoral-fin origin to dorsal-fin origin (0.23), proportional values of which were all greater in T. cryptica.Greatest negative loadings along sheared PC2 were for caudal peduncle length (-0.40), preanal length (-0.27), prepelvic length (-0.25), and eye diameter (-0.25), proportional values of which were all slightly greater in T. atronasus.Additionally, mean ratios that were slightly greater in T. cryptica than in T. atronasus included predorsal length, prepectoral length, body width at pelvicfin origin, and head length.As reflected in number of analfin rays, the anal-fin base length of T. atronasus is shorter than that of T. cryptica.
In the PCA between T. brevis and T. cryptica (Fig. 8c), cumulative variance totaled 94.3% for the first three principal components with 87.2% of that attributed to PC1.Measurements with greatest positive loadings along sheared PC2 were caudal peduncle depth (0.48), caudal peduncle length (0.31), adipose-fin origin to anal-fin insertion (0.23), and body width at pelvic-fin origin (0.21); mean ratios of these variables relative to SL were all greater in T. cryptica than in T. brevis.Measurements with greatest negative loadings along sheared PC2 were snout length (-0.37), upper jaw length (-0.32), lower jaw length (-0.22), and prepectoral length (-0.21).Relative to T. cryptica, T. brevis has a shorter, more slender caudal peduncle, and a more spatulate shaped head and inferior mouth.In the PCA between T. brevis and T. rondoni (Fig. 8d), proportion of variance for the first principal component and cumulatively for the first three principal components totaled 95.0% and 98.0%, respectively.Greatest positive loadings along sheared PC2 were for eye diameter (0.44), anal-fin base length (0.32), pelvic-fin origin to adiposefin origin (0.30), and pectoral spine length (0.28), mean proportional values of which were all greater for T. brevis.Measurements with greatest negative loadings along sheared PC2 were anterior internarial distance (-0.29), gape width (-0.28), head depth at supraoccipital (-0.27), and head width at postorbitals (-0.26), mean ratios of which were all greater for T. rondoni.Among others, measurements with slightly higher mean proportional values in T. rondoni in comparison to T. brevis included preanal length, prepectoral length, and head length.In essence, T. rondoni has a slightly more robust body and head shape than T. brevis.
Size range 72.2-109.9mm SL (n=34) for penuptial and nuptial males.Dorsal profile of head weakly convex from tip of snout to dorsal-fin origin.Dorsal profile of body from behind dorsal fin to caudal fin slightly convex to nearly straight.Abdomen convex from cleithrum to anal-fin origin.Ventral contour of body along anal-fin base angled upward in straight line roughly parallel to dorsal profile of head behind eyes.Caudal peduncle relatively deep, 8.2-12.7%SL.Body not markedly compressed at pectoral-or pelvic-fin base, but rather gradually tapered to base of caudal fin.Head length 25.3-31.2%SL.Mouth subterminal, the upper jaw extending anterior to tip of lower jaw approximately the width of the premaxillary tooth band.Snout short, 36.9-49.5% HL, forming a broad arc in dorsal profile.Posterior edge of lower jaw reaching to just below middle of eye.Premaxillary and dentary tooth bands narrow, teeth small, straight to slightly recurved, not in discrete rows.Eye large, 16.0-27.8%HL, covered by thick epidermis and invested by opaque subepidermal fat deposits on anterior and posterior margins; eyes lateral, equally visible from ventral and dorsal profile (Fig. 1a).Fontanelle groove short, deep, bounded by relatively high ridges on central portion of frontals.Anterior nares lateral to distal tip of mesethmoid wings and directed forward; posterior nares remote, not bordering lateral margins of frontals, each with very short flap of epidermis surrounding entire margin.Gill membranes broadly fused to isthmus along anterolateral margin of cleithrum; pre-isthmus length 66.4-82.5% HL.Branchiostegal rays 7-9 (mode 8; n=51).Total gill rakers on anterolateral margin of first arch 14-23 (mode 16; n=28); first epibranchial with 4-8 (mode 5) gill rakers, first ceratobranchial with 9-15 (mode 11).Longest gill rakers near middle of arch thin, flat, and typically crenulate on medial margin; tapering, short, smooth, and more conical gill rakers near ends of each arch.
Anal fin short, base 22.1-27.6%SL, with 23-30 rays (mode 27; n=97); distal margin straight to slightly convex except in nuptial males.Anal-fin pterygiophores 23-27 (mode 25; n=19).First 5 anal-fin rays of prenuptial and nuptial males unbranched, elongated, and thickened to form intromittent organ; gonopore located distally on leading edge of anal fin about one-third to one-half distance from base to tip of longest ray in prenuptial specimens, to near the tip of the leading ray in fully nuptial specimens.Pectoral-fin spine well developed, short, stout, 13.3-19.0%SL, not reaching to pelvic-fin origin.Anterior margin of spine rugose but lacking distinct serrae.Dorsal and ventral surfaces of spine with shallow longitudinal grooves.Posterior margin of spine with single series of retrorse serrae along entire length except short proximal section; serrae, counted from both sides in some specimens, ranging from 12-26 (mode 19; mean=19.1±2.6 SD; n=112).Pectoral fin with 8-9, rarely 7 branched rays (mode 9; n=100), anterior-most pectoral rays longest.Postcleithral process absent.
Pelvic-fin origin about even with or slightly anterior to vertical plane through tip of adpressed dorsal-fin spine, excluding prenuptial and nuptial males; distal margin of fin straight to slightly rounded.Pelvic fin rays i,6; first branched ray longest, subsequent rays progressively shorter.
Gas bladder of adult large, bulbous anterior margin, tunica smooth over entire surface, moderately turgid and thickened where internal septae contact interior walls, with two relatively short tubular posterior diverticula (Figs.6a, b; see Remarks).Large, rugose Müllerian ramus (Fig. 4) forming expanded discoidal plate, impinging on anterodorsal face of gas bladder.

Color in alcohol.
Overall ground color of body light tan to cream colored.Top of head and dorsum with a dense cast of slate-gray, dark brown, or black melanophores, diminishing sublaterally.Intensity and extent of pigmentation variable, but never appearing mottled or spotted.Freshly preserved specimens usually with dense patches of dusky specks on chin, flanks above anal fin, and an elongate streak in each caudal lobe extending from base of hypural plate to midpoint of longest caudal rays or beyond (Fig. 9).Pigment on chin (Fig. 1a) ranges from a full semicircle of dense specks extending from lower lip to rear margins of orbits, to a faint crescent overlying dentaries, and usually represented by at least traces of subcutaneous flecks scattered between symphysis of the dentaries; in some specimens, especially live or freshly preserved, the chin pigmentation appears as two large, bilateral, intense dark patches.Upper lip and margin of opercular flap with thin streaks of intense black pigment.Pigment on flanks above anal fin variable, usually consisting of relatively light, diffuse, minute melanophores (often obscure or faded in preserved specimens), occasionally consisting of a large dark patch formed by aggregated melanophores.Pigment in upper caudal lobe usually more extensive than in lower caudal lobe; in some specimens, pigmentation at caudalfin base diffuse.Darkly pigmented specimens with a patch of melanophores extending laterally on body posteriorly from top margin of opercular opening onto dorsal half of pseudotympanum, and anterior to pelvic-fin origin.Dorsal fin generally lacking pigment except along anterior margin of fin spine.Adipose fin hyaline except for small patch of melanophores extending from midline onto anterior base of fin.Pectoral, pelvic, anal, and caudal fins with thin bands of black pigment along distal margins.
Distribution.Tympanopleura atronasus is distributed throughout the middle and upper Amazon River basin, including the río Ucayali in Peru, río Mamoré in Bolivia, and mainstem and major tributaries of the rio Solimões and upper rio Amazonas in Brazil (Fig. 10).The species has been taken principally from large main channels and sloughs associated with lowland lotic habitats throughout its range.

Ecology.
Little is known about the life-history or general ecology of T. atronasus.In the material examined, at least 34 prenuptial or nuptial males and 26 gravid females were identified.Based on these specimens, the reproductive period for this species occurs between mid-to-late October and the end of March.The extended period during which reproductive specimens were available presumably represents broad temporal (including interannual) and spatial variability in the rainy season and local conditions across the upper to middle portion of the Amazon River basin where the species is predominately distributed.Males exhibited peak nuptial barbel and dorsal-fin dimorphism from mid December through March.Reproductive males ranged from 72.2-109.9mm SL (mean=91.0;n=34), and ripe females ranged from 60.4-115.7 mm SL (mean=89.7;n=26).Cursory examination of gut contents of a few specimens revealed the presence of small macroinvertebrates and fish remains.
Remarks.Tympanopleura atronasus apparently exhibits some variation in gas bladder morphology, although we did not examine many specimens or conduct a detailed study of variation.Paired posterior (terminal) diverticula separated at their bases, as in Fig. 6a, were observed in other specimens examined by Walsh (1990:94, fig. 20d; UF 44926) and Birindelli et al. (2012:656, fig. 6a; MZUSP 85285, but note apparent error in figure legend), in contrast to more robust, horn-like diverticula, fused at their bases, observed for one specimen illustrated herein (Fig. 6b).Additionally, a specimen (MEPN 302) from the río Yasuni, Ecuador, examined by D. Stewart and R. Barriga-Salazar (pers. comm.), exhibited an anamolous fusion of the posterior ends of paired terminal diverticula, separated at their bases, forming a loop.All of the above specimens were of adult size (79.9-107.3mm SL), thus observed variation was presumed not to be due to differences in developmental stage.A comprehensive study is needed to fully examine the extent of variation in gas bladder morphology in this species, as well as congeners, to determine if there are trends across ontogenetic or size stages, geographic areas, or possible differences between the sexes.
Etymology of the specific epithet is derived from the Latin ater (neuter atrum), meaning black, and nasus, the nose, in reference to the intense black pigmentation on the tip of the snout and lips in live and freshly preserved specimens.We consider the name to be a noun in apposition and therefore follow Article 34.2.1 of the International Code of Zoological Nomenclature (ICZN, 1999)    Head large, length 29.7-35.6%SL, greatly depressed and spatulate anterior to eyes.Dorsal surface of frontals and supraoccipital rugose.Snout long, broadly rounded or squared off anteriorly in dorsal profile.Mouth distinctly inferior, most of premaxillary tooth patch exposed when mouth is closed.Premaxillary and dentary tooth bands relatively broad at midline, teeth sharp, recurved, not in discrete rows.Premaxillary teeth in a series of about 4-5 irregular rows at midline, tapering to 2-3 rows posterolaterally.Dentary tooth patch in a series of 3-4 irregular rows, not tapered laterally.Eye intermediate in size relative to congeners, 13.8-21.0%HL; eyes lateral, slightly more visible from dorsal than ventral profile, covered with thin, translucent skin (Fig. 1b).Fontanelle groove moderate in length, approximately equal to or slightly greater than eye diameter, deep, bounded by relatively high ridges on central portion of frontals.Anterior nares lateral to distal tips of mesethmoid wings and directed forward; posterior nares remote, not bordering lateral margins of frontals, each with very short flap of skin surrounding entire margin.Posterior edge of lower jaw reaching to just below middle of eye.Gill membranes broadly connected to isthmus; preisthmus length 49.5-75.3%HL.Branchiostegal rays 8-9 (mode 9; n=26).Total gill rakers on anterolateral margin of first arch 20-24 (mode 23; n=28); first epibranchial with 7-9 (mode 8) and first ceratobranchial with 13-16 (mode 15) gill rakers.Gill rakers long, crenulate.
Pectoral-fin spine well developed and pungent, long, 19.1-24.4% SL, reaching past origin of pelvic fin when depressed.Anterior margin of spine rugose with single series of low-crowned knobs, most pronounced proximally.Dorsal and ventral surfaces of spine with 2-3 shallow, longitudinal grooves extending the length of the spine.Posterior margin of spine with 14-37 (mode 19; mean=23.5±6.0SD; n=33) sharp, unicuspid retrorse serrae, arranged in single row, or bicuspid or in two distinct parallel rows proximally.Combined, five specimens, the types of T. brevis (NMW 47801), T. alta (CAS 58258 and CAS 58259), and one other specimen (MCZ 36190) had noticeably more posterior pectoral-spine serrations (30-37; mean=33.4;both fins) than all other specimens examined (14-31; mean=21.7;n=28; left fin only); size range of the former group was 93.5-109.0mm SL, and the latter group ranged in size from 43.5-82.0mm SL.This difference in posterior pectoral-spine serrations is provisionally attributed to a possible ontogenetic difference, with larger specimens having a greater number, but the possibility of geographic or inter-population variation cannot be precluded.Pectoral fin with 10-12 (mode 11) branched rays, posterior margin of fin falcate with anterior rays longest.Postcleithral process typically present and moderately robust, short, conical.
Pelvic-fin origin anterior to vertical plane through tip of adpressed dorsal-fin spine; distal margin of fin straight to slightly convex.Pelvic fin rays i,6; first branched ray longest, subsequent rays progressively shorter.
Gas bladder of adult large, cordiform with rounded posterior margin, tunica smooth and thin over entire surface, with two short terminal diverticula joined or closely proximate at their bases (Fig. 6c).

Color in alcohol.
Background coloration tan to yellowishbrown, lighter on venter than on dorsum.Upper sides of body, dorsum, and head peppered with diffuse, small brown specks; melanophores darkest and most densely distributed dorsolaterally.Lower half of sides below lateral line variable, typically lightly speckled.Underside of head and body generally with very little or no pigmentation.Concentrations of melanophores on upper half of opercle and in wedge-shaped areas posterior to eyes along sublateral margin of head.Top of head nearly uniformly pigmented, but with lighter areas surrounding orbits, above fontanelle, and around nares.Top of supraoccipital solid dark brown, extending onto anterior margin of dorsal spine.Base of dorsal fin with brown specks, extending outward along first soft ray; tip of fin dark brown to black.Adipose fin hyaline or opaque.Caudal peduncle with dense concentration of melanophores forming weak crescentic bar; caudal-fin rays generally unpigmented except near base.Anal fin hyaline or only lightly speckled except for occasional thin dark brown or black margin.Pectoral and pelvic fins similarly pigmented, black posterior margin and stripe extending along top of first 3-4 rays, darkest near tips of rays, lightly speckled along ray margins and near base of remaining fin rays.
Distribution.Tympanopleura brevis is distributed throughout the middle and upper Amazon River basin, with most records from the State of Amazonas in Brazil and the Loreto Region of Peru (Fig. 12).Ecology.Pouilly et al. (2003Pouilly et al. ( , 2004) and Pouilly & Rodriguez (2004) reported Tympanopleura brevis (as Ageneiosus brevis), together with an unidentified species listed as Tympanopleura sp., from floodplain lakes of the río Mamoré, Bolivia.These authors examined species assemblages, habitat characteristics, and diet composition of species in the fish communities, and reported Tympanopleura as occurring in three lake types: oxbow lakes immediately adjacent to the río Mamoré mainstem, forested floodplain lakes (> 1 km from the mainstem river), and floodplain edge lakes (> 4 km from the mainstem).Based on diet composition and breadth, these investigators scored T. brevis as a zooplanktivore (diet comprised primarily of rotifers and microcrustaceans), with aquatic invertebrates as secondary in importance (Pouilly et al., 2004, Table 2), and stated "Ageneiosus brevis appears to be the only species that is highly specialized in the consumption of zooplankton" (Pouilly et al., 2003(Pouilly et al., , p. 1143)).In their tabular summaries, T. brevis was assigned an abbreviation of "AGEMA" whereas Ageneiosus inermis was assigned a species code of "AGEBR," but diet composition was not reported for the latter.Diet classification for "AGEBR" (as a piscivore/carnivore) was derived from bibliographic references (Santos, 1991;Marrero & Taphorn, 1991).We suspect that there may have been transposition of data regarding species codes and/or diet composition as reported by these authors.A few gut contents of specimens of different species of Tympanopleura examined by the senior author all contained prey items larger than microcrustaceans, primarily aquatic macroinvertebrates (especially decapods) and fish remains.We did not examine any auchenipterid specimens obtained in the río Mamoré study (Pouilly et al., 2003(Pouilly et al., , 2004;;Pouilly & Rodriguez, 2004), and thus cannot confirm the identity of specimens assigned to "A. brevis" or the diets of specimens attributed to this species in their study.
Remarks.Tympanopleura brevis was described by Steindachner (1881) from four specimens ranging in length from 4 to 4.5 in (10.2-11.4cm), presumably TL.Only two specimens from the original type series were located (NMW 47801), and we determined that both of these specimens represent the same species.We hereby select the larger specimen of this lot, a 104.0 mm SL presumed female, based on size of the maxillary barbel, as a lectotype .The current disposition of the other two specimens from the type series is unknown.
A single specimen (IU 15790, 135 mm, presumably TL) was designated as the type in the original description of T. alta (Eigenmann & Myers, in Myers, 1928), and the collection locality was listed as "Iquitos, Rio Marañon Peru."Subsequently, Eigenmann & Allen (1942) redescribed T. alta and listed as the type IU 15790, 132 mm, and as a paratype IU 15977, 128 mm, both from Iquitos.The city of Iquitos is not on the río Marañon proper, however, and the precise locality from where these specimens were collected is unknown.Lucinda et al. (2007) reported Ageneiosus brevis in a list of species from a survey of fishes in the vicinity of the Lajeado Hydroelectric Reservoir on the rio Tocantins, State of Tocantins, Brazil.No specimens of T. brevis were represented from the rio Tocantins or other major tributaries of the lower Amazon River basin in the material examined herein.Thus, we conclude that the specimens reported as A. brevis by Lucinda et al. (2007) were either misidentified or represent a significant range extension of T. brevis as currently documented.
Etymology of the specific epithet is from the Latin brevis, meaning short, possibly in reference to the relatively short head in comparison to Ageneiosus inermis, to which Steindachner (1915) compared this species.
Description.Tympanopleura cryptica is a small-sized auchenipterid.Specimens of undetermined sex, mature females, and non-nuptial males ranged in size from 35.0-78.2mm SL (n=29).Prenuptial and nuptial males ranged in size from 57.5-84.9mm SL (n=15).Morphometric data are summarized in Table 10.Dorsal profile of head nearly straight or weakly convex to dorsal-fin origin.Dorsal profile of body from behind dorsal fin to caudal fin slightly convex to nearly straight.Body relatively short, depth at base of dorsal fin approximately equal to or slightly greater than body width at origin of pectoral fin.Ventral profile of head flat, ventral profile of body from isthmus to anal-fin origin straight or gently rounded, angled upward posteriorly along anal-fin base.Caudal peduncle deep, 8.3-11.4% SL.Body not markedly compressed at pectoralor pelvic-fin base, but rather gradually tapered to base of caudal fin.
Head length 25.9-33.0%SL.Mouth only weakly inferior, upper jaw projecting anterior to tip of lower jaw a distance approximately equal to width of the premaxillary tooth band and less than half of eye diameter.Corners of mouth approximately in line with transverse plane extending between posterior nares; posterior edge of lower jaw extending to a point approaching a plane through middle of the eye.Snout short, 40.4-51.3%HL, forming a broad arc or squared off in dorsal and ventral view.Jaw teeth small, conical, slightly recurved, barely extending through epidermal tissue.Center of premaxillary tooth plate partially to fully exposed in ventral view, fully exposed posterolaterally, with about 3-6 irregular rows of teeth at midline, tapering to 1-2 rows posterolaterally.Dentary teeth small, thin, conical, distributed in about 3-4 uneven rows and slightly exposed laterally.Eye relatively large, horizontal diameter 16.7-25.6%HL, covered by thick epidermis; eyes lateral, equally visible in dorsal and ventral view (Fig. 1c).Cranial fontanelle relatively elongate, open from posterior margin of mesethmoid along anteromedial half of frontals to a point just anterior to a plane passing through posterior margins of the eyes.Anterior nares lateral to distal tips of mesethmoid wings and directed anterodorsally; posterior nares remote, about equidistant between anterior nares and anterior margin of orbit, encircled by short ridge of epidermis.Gill membranes broadly fused to isthmus along a plane falling posterior to rear margin of orbit, pre-isthmus length about 62.5-82.8%HL.Branchiostegal rays 7-8 (mode 8; n=19).Total gill rakers on anterolateral margin of first arch 21-26 (mode 22; n=23); first epibranchial with 6-10 (mode 8) and first ceratobranchial with 13-20 (mode 14) gill rakers.Longest gill rakers near middle of arch thin and crenulate on medial margin; tapering, short, and pointed near distal ends of each arch.
Maxillary barbel of females and non-nuptial males small, filamentous, concealed in premaxillary groove, length 13.9-15.8%HL (mean=15.1±0.8SD; n=6).Maxillary barbel of prenuptial males ossified and slightly thickened over approximately proximal one-half to threefourths, with fleshy terminus, extending slightly beyond rictus, lacking well-developed hooks, length 21.2-29.6%HL (mean=24.1±2.7 SD; n=11).Structure of nuptial male maxillary barbel unknown, as no peak nuptial males were available in material examined.Dorsal fin rays II,6, consisting of a small spinelet, elongated spine, and branched rays; first ray longest, extending anterior to or about equal to midpoint between dorsal-fin origin and adipose-fin origin when fin is adpressed.Dorsal-fin spine short, relatively thin and weak in females and non-nuptial males, depressed spine reaching less than midpoint between dorsal-fin origin and adiposefin origin, length of spine 16.8-22.3%SL (mean=20.2±1.6 SD; n=10).Dorsal-fin spine elongated in prenuptial and nuptial males, 18.6-34.9%SL (mean=23.5±4.6 SD; n=13).Serration of spine variable.In females and nonnuptial males, anterior margin of spine weakly to strongly crenulated with single row of low-crowned serrae (range 12-33; mean=22.9±6.1 SD; n=15), crowded together proximally and forming a low embedded keel, more distantly separated distally, or absent altogether over distal half or more.Dorsal, ventral, and lateral margins of spine with well developed longitudinal grooves and ridges.Posterior margin of spine in females and non-nuptial males with 13-24 weak serrae (mode 20; mean=18.7±3.0SD; n=18); serrae short, relatively blunt, absent near base, displaced to ventrolateral edge of spine in some specimens, and occasionally nearly absent on entire posterior margin.Detailed structure of dorsal-fin spine of nuptial males unknown; one prenuptial male examined (USNM 270812; 72.2 mm SL) with entire anterior margin of dorsal-fin spine crenulated, denticulations longest and most closely spaced proximally, but lacking well developed serrae; posterior margin weakly crenulated proximally and smooth distally.Longest dorsal-fin rays reaching well beyond tip of spine in all but prenuptial and nuptial males.Adipose fin small, posterior margin free.
Anal fin relatively short, base 24.4-30.3%SL, with 23-30 rays (mode 29; n=39); distal margin gently convex in juveniles, females, and non-nuptial males.Anal-fin pterygiophores 25-28 (mode 27; n=25) in specimens examined with ≥ 27 anal rays.First 5 anal-fin rays of prenuptial males unbranched, elongated, and thickened to form intromittent organ; gonopore located distally on leading edge of anal fin about one-third to one-half distance from base to tip of longest ray, presumably displaced toward distal end in fully nuptial male.
Gas bladder of adults large, cordiform, posterior margin blunt, tunica smooth and thin over dorsal, lateral, and anteroventral surfaces.Exterior posteroventral surface of tunica thickened, with weak, irregular, posterolaterally radiating ridges as in T. piperata.Two short terminal diverticula joined or weakly proximate at their bases (Fig. 6d).

Color in alcohol.
Base color of head and body dark brown, gray, or tan with pigmentation generally of relatively uniform shading.Top and sides of head, dorsum, upper half of sides of body with dense pigmentation consisting of small brown to black melanophores, darkest on head, anterolaterally, and dorsally.Pigment on sides of head extends anterior to eye, on membrane over eye, and on opercular skin slightly posteroventrally to eye.Lower half of sides of body with pigment less intense, but extending to base of anal fin and most concentrated anteriorly, especially over pseudotymanum and above pectoral-fin base.Pigment never appearing mottled or spotted.Chin in some specimens with an intense crescent or half-moon shaped patch of dark, concentrated brown melanophores, similar to T. atronasus.Streaks of brown pigment in dorsal and pectoral fins, most intense along leading edge of anterior-most ray; dorsal-fin spine and pectoral-fin spines with flecks scattered along anterior and lateral margins in the former, and anterior and top margins in the latter.Brown pigment extending from sides of body onto base of caudal fin, forming a broad, weakly defined vertical patch, somewhat darker and slightly crescent shaped in upper lobe.Adipose fin with melanophores scattered throughout.Anal and pelvic fins generally hyaline, but the latter with a small patch of melanophores above base of the anterior rays.
Distribution.Tympanopleura cryptica is known from relatively few records in the middle and upper Amazon River basin, State of Amazonas in Brazil and the Loreto Region of Peru (Fig. 12).

Tympanopleura longipinna, new species
Description.Morphometric data are summarized in Table 11.A small-sized auchenipterid.Size range 34.2-81.3mm SL (n=108) for specimens of undetermined sex, mature females, and non-nuptial males.Size range 50.5-69.2mm SL (n=14) for prenuptial and nuptial males.Head moderately depressed, dorsal profile weakly convex to dorsal-fin origin.Dorsal profile of body from behind dorsal fin to caudal fin nearly straight or slightly convex.Isthmus and abdomen flat or slightly convex to pelvicfin origin.Ventral contour of body along anal-fin base angled in a straight line upward to the caudal peduncle.Caudal peduncle relatively shallow, 6.6-9.7%SL.Body moderately compressed at pectoral-fin insertion, strongly compressed posterior to pelvic-fin base.Head length 25.2-29.7%SL.Mouth weakly inferior.Snout relatively long, 40.3-57.1% HL, broadly parabolic in dorsal profile.Premaxillary and dentary tooth bands relatively narrow, teeth minute, conical to weakly recurved, in an irregular series of about 4-5 rows medially on the premaxilla, tapering to 2-3 rows, about 2-3 medially on dentary.Eye moderate in size, 11.6-18.5% HL, covered by relatively thin layer of epidermis; eyes lateral, equally visible from dorsal and ventral profile (Fig. 1d).Fontanelle groove moderately large, recessed, extending from mesethmoid along most of medial margins of frontals posteriorly to a plane approximately in line with the posterior edges of the orbits.Anterior nares lateral to distal tip of mesethmoid wings and directed forward; posterior nares remote, not bordering lateral margins of frontals, with a low epidermal flap around margin, raised slightly posteriorly.Posterior edge of lower jaw reaching to just below middle of orbit.Gill membranes broadly fused to isthmus behind plane through rear margin of orbit.Branchiostegal rays 8-9 (mode 8; n=30).Total gill rakers on anterolateral margin of first arch 19-25 (mode 23; n=29); epibranchial with 7-9 (mode 9) and ceratobranchial with 12-17 (mode 14) gill rakers.Longest gill rakers near middle of arch thin and crenulate on medial margin; gill rakers tapering, short, and pointed near ends of each arch.
Maxillary barbels of females and non-nuptial males minute, filiform, concealed in premaxillary groove, length 8.6-28.9%HL (mean=15.5±5.3SD; n=24).Barbel of prenuptial males thickened, elongated, ossified most of length, with fleshy tip.Barbel of nuptial males ossified entire length, curved inward toward side of head when adducted.Barbel length of prenuptial and nuptial males 35.8-52.1% HL (mean=45.0±5.1 SD; n=8).Barbel of prenuptial and nuptial males with 5-15 (mode 13; n=8) incipient hooks on anterodorsal and posterolateral surfaces; hooks fully ossified, sharp, recurved in peak nuptial males.Hooks appear to begin development first on the anterodorsal margin, numbering 5-8 in the material examined, with 0-9 on the posterolateral margin.Dorsal fin rays II,6, consisting of a small spinelet, elongated spine, and branched rays; first ray longest, tip extending anterior to midpoint between dorsal-fin origin and adipose-fin origin when fin is adpressed.Dorsal-fin origin about equal with vertical plane passing through pectoral-fin insertion.Dorsal-fin spine short, relatively thin and weak in females and non-nuptial males, depressed spine reaching about one-third or less the distance between dorsal-fin origin and adipose-fin origin, length of spine 13. n=24).Anterior margin of dorsal-fin spine weakly to moderately crenulated with single row of low-crowned denticulations.Lateral margins of spine with distinct longitudinal grooves and ridges.Entire posterior margin with 16-29 (mean=21.4±3.9SD; n=16) relatively small, conical, retrorse serrae.Dorsal-fin spine of prenuptial and nuptial males (56.1-69.2mm SL) elongated, thin, nearly straight, 18.6-37.8%SL (mean=29.0±6.1 SD; n=8), with 35-56 (mean=46.3±9.0;n=4) sharp, antrorse serrae along anterior margin; serrae arranged in an alternating anterolateral direction on distal half of spine, those on proximal section of the spine in serial row or directed less acutely anterolaterally, irregular and more densely spaced, embedded basally within a ridge of integument.Posterior margin of dorsal-fin spine in nuptial males nearly smooth or with about 18-39 minute, irregularly spaced denticulations.Adipose fin small, posterior margin free.
Anal fin long, base 33.9-39.9%SL, with 32-42 rays (mode 37; n=74), distal margin straight except in nuptial males.Anal-fin pterygiophores 32-38 (mode 34; n=27).First 5 anal-fin rays of prenuptial and nuptial males unbranched, elongated, and thickened to form intromittent organ; gonopore located distally on leading edge of anal fin about one-third to one-half distance from base to tip of longest ray.
Pelvic-fin origin slightly posterior to tips of longest adpressed pectoral-fin rays; distal margin of fin straight to slightly convex.Pelvic fin rays i,6; first branched ray longest, subsequent rays progressively shorter.
Pseudotympanum large, triangular, opaque to semitranslucent, weakly to unpigmented on exterior surface.Gas bladder of adult large, cordiform, thin-walled with slightly conical posterior margin, tunica smooth over entire surface, with two short terminal diverticula separated at their bases (Fig. 6e).

Color in alcohol.
Overall base color of body light tan to cream colored, pigmentation in most specimens relatively light.Minute, diffuse brown melanophores on top and sides of head, over pseudotympanum, forming a narrow middorsal stripe, and occasionally scattered on sides above lateral line.Concentration of pigmentation greatest over supraoccipital and frontals, around base of dorsal-fin spine, including anterior margin of spine proximally, and middorsal stripe.Pigmentation in some specimens irregular on top of head and mid-dorsally, forming a weakly mottled appearance.Fins, venter, and chin unpigmented.
Distribution.Tympanopleura longipinna is broadly distributed throughout the upper and middle Amazon River basin in Brazil and Peru (Fig. 15).Etymology.The specific epithet longipinna is derived from the Latin longus, meaning long or extended, in combination with the Latin pinna, referring to fin.The name is in reference to the long, multi-rayed anal fin of this species relative to congeners, treated as a noun in apposition.Gender feminine.
Remarks.Tympanopleura longipinna has been misidentified in the past, or its distinctiveness from congeners not readily recognized, based on its superficially similar appearance to other species in pigmentation pattern and general morphology.Walsh (1990) erroneously included specimens of T. longipinna, together with specimens of T. rondoni, in his account of T. brevis (as Ageneiosus brevis), although at the time he concluded that there was likely more than one taxon involved.A substantial increase in the amount of available study material in recent years, including many specimens collected during the "Calhamazon" expeditions, has made it possible to evaluate the morphology of this taxon in greater detail.The species is diagnosed on the basis of a combination of relatively subtle characters by which it clearly differs from congeners, e.g., composite bodyshape differences as listed under Diagnosis and revealed by multivariate analysis (Fig. 8a) and high anal-fin ray count.Eigenmann, 1912 Figs. 1e, 5, 6f, 16, 17 Tympanopleura piperata Eigenmann, 1912: 203-204, pl. 20 [typelocality: -British Guiana (=Guyana) Additionally, unlike T. piperata, T. rondoni has a heavily spotted pigmentation pattern and an elongated gas bladder with a pair of long, recurved diverticula.Snout moderately short, 31.4-43.6%HL.Anterior margin of upper jaw weakly rounded to squared off in dorsal profile.Premaxillary and dentary tooth bands narrow, teeth small, conical.Premaxillary teeth in a series of about 2-4 irregular rows at midline, tapered to 1-2 rows on lateral edges, posteriormost area of premaxilla devoid of teeth.Dentary tooth patch in an irregular series of about 3-4 rows.Eye large, 24.3-35.7%HL, nearly equally visible from dorsal and ventral profile, covered by thin layer of epidermis (Fig. 1e).Posterior edge of lower jaw approximately below middle of eye.Fontanelle groove relatively short, extending from posterior margin of mesethmoid to a point anterior to the plane passing through the rear margins of the orbits.Anterior nares just lateral to tips of mesethmoid wings; posterior nares offset from central margin of mesethmoid.Gill membranes broadly fused to isthmus at anterolateral margins of cleithra.Branchiostegal rays 7-8 (mode 7; n=35).Total gill rakers on anterolateral margin of first arch 16-23 (mode 19; n=28); epibranchial with 5-9 (mode 6) and ceratobranchial with 10-15 (mode 12) long, thin gill rakers.
Pelvic-fin origin anterior to vertical through tip of longest adpressed dorsal-fin ray; margin of fin straight to slightly rounded.Pelvic fin rays i,6; first branched ray longest, subsequent rays progressively shorter.
Pseudotympanum large, ovoid, semi-translucent, epidermis covering muscle hiatus bulging outward and variably pigmented on exterior surface, ranging from nearly hyaline to moderately pigmented, especially on dorsal half (Figs. 5,16); projected light visible between sides due to the size and transparency of the gas bladder and thin overlying epidermis.Gas bladder of adult large, cordiform, apple shaped, moderately turgid, smooth-walled on dorsal, lateral, and anteroventral margin; posteroventral margin with an inverted "V" shaped thickened area of tunica with weak to moderate external ridges (Fig. 6f).No terminal diverticula.Internal median septum thin, laminar, together with posteroventral margin of gasbladder capsule weakly ossified in adults (Fig. 17).
Table 12.Morphometric data for specimens of Tympanopleura piperata.Synoptic material includes the holotype and six paratypes of T. piperata (FMNH 53244,CAS 58382[3], MCZ 30189, BMNH 1911.10.31.102)Color in alcohol.The description and illustration in Eigenmann (1912: 204, plate 20, fig. 3; reproduced here in Fig. 16b) indicates the holotype of T. piperata, as the specific epithet alludes, to originally have relatively uniform "peppered" pigmentation over the head, dorsum, and sides of body, with dense concentrations of melanophores at the base of the caudal fin, base of the dorsal fin, over the pseudotympanum, and tip of the snout.The preserved holotype is now faded, and, due to shrinkage, it is now difficult to discern pigmentation pattern.In freshly collected specimens, the background color is typically tan to beige or dusky yellowish, with many specimens showing sparse traces of pigmentation.
In well-pigmented individuals, the dorsum, sides of the body, and the head are covered with diffuse minute brown specks consisting of individual melanophores, occasionally enlarged or coalesced and forming weak spots or slight mottling.A prominent hourglass-shaped vertical bar at the base of the caudal fin, consisting of fine, densely clustered brown or black melanophores, is characteristic of this species (Fig. 16b); the leading vertical edge of the bar is nearly straight.Pigment on dorsal aspect of body generally confined to a relatively narrow stripe, sometimes broken into irregular patches, extending down midline of back and with scattered specks distributed ventrally above lateral line and over pseudotympanum.Venter generally depigmented, occasionally with melanophores dispersed on chin, isthmus, and lower portion of opercula and body near pectoral-fin base.Top and sides of head moderately and irregularly pigmented, with some light areas around nares, between orbits, and on lower half of opercula.Skin above supraoccipital generally brownish, somewhat more intense at base of dorsal spine.Pigment extending along part or most of anterior margin of the dorsal spine.Dorsal fin only lightly pigmented, occasionally with distal tips of rays darkened.Adipose and distal portion of caudal-fin lobes hyaline or only lightly speckled.Anal fin generally with little pigment, but in some specimens with thin black margin, most intense at distal tips of anterior rays.Pectoral and pelvic fins dusky, with melanophores concentrated along anterior rays and interradial membranes, near base, and occasionally along distal margin of fin.
Distribution.Tympanopleura piperata is distributed in the Essequibo River drainage of Guyana, including the Potaro and Rupununi rivers, and in the central and upper Amazon River basin in Brazil and Peru (Fig. 15).
Maxillary barbel of females and non-nuptial males small, ossified at base, filiform, concealed in premaxillary groove, 9.6-26.8%HL (mean=16.2±4.1 SD; n=25); groove extending obliquely to midpoint between corner of mouth and front of eye.Maxillary barbel of prenuptial and nuptial males ossified most or all of length, thickened, elongated, 30.n=12).Barbel of prenuptial males smooth, with a fleshy tip, covered with thin epidermis, and lacking hooks altogether or with few (about 6-8) small, blunt, incipient hooks beginning development on anterodorsal surface.Maxillary barbel of nuptial male with 10-17 (n=3, including left and right in one specimen) sharply pointed, recurved hooks, modally 9 on anterodorsal margin, 4-10 on ventromedial margin; entire barbel with thick epidermal sheath covering all but tips of hooks.Dorsal fin rays II,6, consisting of a small spinelet, elongated spine, and branched rays; first ray longest, subsequent rays progressively shorter.Dorsal-fin origin about equal with or slightly posterior to vertical passing through pectoral-fin insertion.Dorsal-fin spine relatively long and stout in females and non-nuptial males, length 17.2-25.0%SL (mean=19.8±2.2SD; n=17).Anterior margin of spine variable, from nearly smooth to strongly crenulated proximally; spine most rugose in larger individuals.Posterior margin of spine in all but nuptial males with 15-38 relatively short, conical, retrorse serrae.Dorsal spine of nuptial male robust, greatly elongated, sinusoidal, anterior margin convex over basal half, inflected posteriorly near midpoint, convex again distally, tip slightly curved laterally; length of spine in pre-nuptial and nuptial males 25.5-40.9%Table 13.Morphometric data for specimens of Tympanopleura rondoni.Synoptic material includes the lectotype and paralectotype of Ageneiosus rondoni (MNRJ 962 [2]) and holotype (FMNH 58143)  Posterior margin of spine in fully nuptial males smooth.Adipose fin relatively large, entire base well anterior to vertical through anal-fin insertion, posterior margin free.Anal fin relatively short, base 23.1-32.5% SL, with 28-37 rays (mode 31; n=63); distal margin rounded.Anal-fin pterygiophores 27-36 (mode 29; n=45).First 5-6 anal-fin rays of pre-nuptial and nuptial males thickened, elongated, unbranched, coalesced to form intromittent organ.
Pelvic-fin origin anterior to vertical through tip of longest adpressed dorsal-fin ray; margin of fin straight to slightly convex.Pelvic fin rays i,6; first branched ray longest, subsequent rays progressively shorter.
Gas bladder of adult large, unencapsulated, elongated antero-posteriorly in comparison to congeners, moderately turgid, smooth-walled on external surfaces, with two moderately elongated fleshy terminal diverticula, close at their bases and typically recurved anteriorly in body cavity (Fig. 6g).
Color in alcohol.Background color tan, dusky yellow, or whitish purple, obscured in many specimens by dark pigmentation over most of dorsum.Distinctive pigmentation pattern consisting of dark brown to black irregular spots (usually 1-2 mm in diameter) over most of body, usually heavily concentrated on head and upper half of body.Spots consisting of coalesced melanophores and often obscured on head and dorsum by additional dense speckles of pigmentation.Spots on body sometimes forming irregular rows along midline of back, sides above the lateral line, and a lower row extending posteriorly from above the pectoral-fin base.Skin lateral to gas bladder darkly pigmented.Venter generally lightly pigmented with specks sometimes near tip of chin and extending along lateral branchiostegal membranes and near pectoral fin.Top of head with dense background of brown or black pigmentation overlain with spots.Leading edge of dorsal-fin spine brown to black; rays of dorsal fin with pigmentation at base and near tips, most heavily concentrated on anterior rays.Adipose fin with uniformly distributed melanophores, more evident near base.Caudal peduncle and base of caudal-fin rays darkly pigmented with a few specks scattered along rays and interradial membranes, sometimes with additional concentrations of pigment at tips of rays.Anal fin with dark margin and some specks scattered along base.Pectoral and pelvic fins pigmented on dorsal surface, most heavily along base, over first few anterior-most rays, and along ray tips forming a distinctive black or brown marginal edge.
Distribution.Tympanopleura rondoni is broadly distributed in the central Amazon River basin, including the rio Madeira in Brazil, and the río Mamoré and río Guaporé in Bolivia (Fig. 19).Remarks.Miranda Ribeiro (1953) cited two cotypes and designated "Lectótipo-A," presumably to fix the name by designating as a lectotype the larger of the two specimens in the type series.However, in a subsequent type catalog, Miranda Ribeiro (1962) referred to only one specimen, listed under MNRJ 962.The specific epithet is a patronym named in honor of Cândido Mariano da Silva Rondon , famous Brazilian Army Marshal ("Marechal"), pioneering telegraph engineer, patriot, zealous explorer, and protector of indigenous tribes.

Fig. 8 .
Fig. 8. Scatter plots of principal component scores from sheared principal component analysis of 29 morphometric variables for: (a) all species of Tympanopleura combined, and two-way comparisons of (b) T. atronasus and T. cryptica, (c) T. brevis and T. cryptica, and (d) T. brevis and T. rondoni.

Fig. 10 .
Fig. 10.Distribution of Tympanopleura atronasus based on material examined.Type-locality unknown.Some symbols represent more than one lot or locality.

Fig. 12 .
Fig. 12. Distribution of Tympanopleura brevis based on material examined (squares; open square represents typelocality), T. cryptica (diamonds; open diamond represents type-locality), and both species in sympatry (open circles).Some symbols represent more than one lot or locality.

Fig. 15 .
Fig. 15.Distribution of Tympanopleura longipinna (stars) and T. piperata (inverted triangles) based on material examined.Open symbols indicate type localities.Some symbols represent more than one lot or locality.

Fig. 17 .
Fig. 17.Ossification of the median septum and tunica of the gas bladder in Tympanopleura piperata.(a) UF 181564 (33.5 mm SL), cleared/stained; (b) INHS 36738 (40.0 mm SL), nuptial male, radiograph.Scale bars = 5 mm.Description.Morphometric data are summarized in Table12.Tympanopleura piperata is the smallest species of the genus.Size range 23.0-47.5 mm SL (n=80) for immature specimens, females, and non-nuptial males.Size range 38.5-46.9mm SL (n=11) for pre-nuptial males.No peak nuptial males were examined.Dorsal profile of head and nape gently sloping upward, nearly straight or slightly concave from tip of snout to base of dorsal-fin spine.Head depressed but not greatly flattened; head relatively deep at midpoint of supraoccipital, 54.3-69.7%HL.Dorsal profile of body posterior to dorsal fin slightly convex to base of upper caudal-fin lobe.Caudal peduncle moderately deep, 7.6-10.5%SL.Body widest at origin of pectoral fin, gradually tapering in width to base of caudal fin.Head length 22.2-27.8%SL.Mouth subterminal, upper jaw extended only slightly anterior to tip of lower jaw.Snout moderately short, 31.4-43.6%HL.Anterior margin of upper jaw weakly rounded to squared off in dorsal profile.Premaxillary and dentary tooth bands narrow, teeth small, conical.Premaxillary teeth in a series of about 2-4 irregular rows at midline, tapered to 1-2 rows on lateral edges, posteriormost area of premaxilla devoid of teeth.Dentary tooth patch in an irregular series of about 3-4 rows.Eye large, 24.3-35.7%HL, nearly equally visible from dorsal and ventral profile, covered by thin layer of epidermis (Fig.1e).Posterior edge of lower jaw

Table 1 .
Frequency distribution of anal-fin rays among species of Tympanopleura.Sample mean values with different letter superscripts are significantly different (p≤0.01);SD = standard deviation.

Table 2 .
Frequency distribution of pectoral-fin rays among species of Tympanopleura.

Table 3 .
Frequency distribution of total gill rakers on anterolateral margin of first arch among species of Tympanopleura.

Table 4 .
Frequency distribution of number of preanal vertebrae among species of Tympanopleura.Sample mean values with different letter superscripts are significantly different (p≤0.01);SD = standard deviation.

Table 5 .
Frequency distribution of total number of vertebrae among species of Tympanopleura.Sample mean values with different letter superscripts are significantly different (p≤0.01);SD = standard deviation.

Table 6 .
Frequency distribution of pairs of pleural ribs among species of Tympanopleura.Sample mean values with different letter superscripts are significantly different (p≤0.01);SD = standard deviation.

Table 7 .
Variable loadings for within-group size factor and sheared principal components representing 29 morphometric variables from a principal component analysis (PCA) of six Tympanopleura species combined.

Table 9 .
34.8-53.6%HL),smallereyediameter,presence of short posterior diverticula on the gas bladder (vs.diverticula absent), and lack of an hourglass-shaped transverse bar of pigmentation usually present at the base of the caudal fin in T. piperata.The relatively uniform pigmentation pattern on the head and body of T. brevis distinguishes it from T. rondoni, which characteristically has a pigmentation pattern consisting of discrete, irregular, large spots distributed over the head, body, and fins.Tympanopleura brevis further differs from T. rondoni in having more anal-fin rays (31-36, mode 33 vs. 28-37, mode 31), fewer gill rakers (20-24, mode 23 vs. 24-33, mode 29-30) more pleural rib pairs (5 vs. 4-6, mode 6), a larger eye diameter (13.8-21.0%HL vs. 8.4-17.0%HL),and a cordiform gas bladder with shorter posterior diverticula (vs.gas bladder elongated antero-posteriorly and with two longer, recurved posterior diverticula).Morphometric data are provided in Table9.Tympanopleura brevis is a relatively small auchenipterid, most specimens not exceeding 100 mm SL; largest specimen examined 109.0 mm SL (holotype of T. alta).Size range 43.5-109.0mmSL(n=64) for specimens of undetermined sex, mature females, and non-nuptial males.Size range 58.4-82.0mmSL(n=5) for prenuptial and nuptial males.Body short, head spatulate.Dorsal profile of head greatly depressed anterior to eyes, acutely angled upward from rear margin of fontanelle to dorsal origin, concave, especially in nuptial males.Body moderately broad at pectoral-fin base, markedly compressed posteriorly to caudal peduncle.Body depth at dorsal fin origin 19.6-23.3%SL.Dorsal contour from dorsal fin to caudal fin nearly straight to weakly convex.Ventral profile from snout to anal-fin origin weakly convex.Caudal peduncle shallow, maximum depth 6.6-10.2%SL.Morphometric data for specimens of Tympanopleura brevis.Synoptic material includes the lectotype and paralectotype of Ageneiosus brevis (NMW 47801[2]) and holotype and paratype of T. alta (CAS 58258, CAS 58259).
and seven paratypes (FMNH 58144) of A. madeirensis.SD=standard deviation.SL (mean=30.6±4.3SD;n=10).Prominent antrorse serrae on anterior margin of spine in pre-nuptial and nuptial males; serrae shorter and relatively blunt proximally early in development of armature, becoming long, thin, recurved, and alternating laterally over distal half, embedded in thick sheath of epidermis.Lateral margins of spine with pronounced longitudinal ridges and deep furrows, obliquely distributed along length of spine, heavily pigmented.