Description of two new species of Physopyxis and redescription of P . lyra ( Siluriformes : Doradidae )

The genus and species Physopyxis lyra was originally described based on only one very distinctive specimen. Analysis of a larger number of specimens provided a more precise characterization of the genus and the type species. Additionally, two new species are described based on material already available in museums and new collections. Physopyxis lyra is characterized by having a well developed coracoid process with divergent tips, and only one series of spines on the lateral plates. Physopyxis ananas, new species, has a thin coracoid process, convergent, and more than one series of spines on the lateral plates. Physopyxis cristata, new species, is a slender species, characterized by an incomplete series of lateral plates and the presence of a middorsal series of spines formed by the tips of the vertebral neural spines. The poorly known geographic distribution of the genus Physopyxis is vastly enlarged to include various drainages of the Amazon and Essequibo basins.


Introduction
The Doradidae is a South American catfish family easily recognized by the presence of spiny bony plates along the lateral line.Currently, the family comprises 72 valid species in 30 genera (Sabaj & Ferraris, 2003).The monotypic genus Physopyxis Cope, 1871, is a remarkable minute doradid with adults not known to exceed 31 mm SL.Physopyxis lyra has always been easily recognized.Cope's original description, however, depicts some morphological discrepancies with the unique type and other P. lyra specimens.For instance, Cope diagnosed Physopyxis lyra by the absence of an adipose fin, and his statement was accepted by Eigenmann (1925) and Burgess (1989).However, the type specimen is in very poor condition (i.e., completely desiccated) and it is difficult to determine whether an adipose fin was originally present.The vast majority of the specimens of P. lyra examined in this study do show an adipose fin.Higuchi (1992) pointed out that there were some discrepancies between the illustration and the text in Cope's (1872) expanded description of P. lyra (Fig. 1).The illustration shows an unnamed structure connecting the posterior nuchal plate to the base of the pelvic fin.This structure is neither present in the holotype nor in any of the examined specimens.The illustration of the anal fin in P. lyra also is exceedingly quadrangular, different from that of all other examined specimens.
Material recently collected and assigned to P. lyra has considerably expanded the geographic distribution of the taxon and raised some doubts about the monotypy of the genus.In this paper, we present a taxonomic review of Physopyxis, with a redescription of P. lyra and descriptions of two new species, and comment on morphological variation observed in the group.

O F S Material and Methods
We examined 2250, and measured 346, specimens of Physopyxis.Most measurements and counts follow Higuchi et al. (1990) and Sabaj (2002), and measurements were taken to 0.01 mm with a digital caliper under a stereomicroscope.Additional measurements are: lateral plate depth -depth of 5th plate (modified from Sabaj, 2002); superior wing depth -depth of superior wing of 5th plate, taken from the dorsal-most exposed contour of plate to point of lateral line spine (modified from Sabaj, 2002); inferior wing depth -depth of inferior wing of 5th plate, taken from the ventral-most exposed contour of plate to point of lateral line spine; body depth at 5th plate -greatest body depth at 5th plate; scapular girdle width -greatest body width at cleithra; postcleithral (humeral) process length -length from anteriormost point of contact between supracleithrum and cleithrum to tip of postcleithral (humeral) process; coracoid process length -length from posteriormost border of pectoralfin point of insertion to tip of the coracoid process; pectoral girdle mesial suture -greatest longitudinal measure of the mesial suture between cleithra and coracoid; distance between coracoid process tips -shortest ventral distance between the tips of coracoid processes; coracoid width -width at external most sides of coracoids at the level of origin of the pectoral fin.Measurements were taken, whenever possible, on the left side of the body and were treated as percents of the standard length (SL).Cephalic measures, such as head depth, snout length, orbital diameter, interorbital distance and mouth width were treated as percents of the head length (HL).
Caudal-fin ray counts follow Lundberg & Baskin (1969).In double-stained specimens examined, principal caudal-fin rays (those that articulate with the parhypural and hypurals) usually include one long unbranched ray in the upper lobe and all the subsequent branched rays.However, in some specimens it was observed that branched rays can also be found on the lower lobe ventral to the hypural plate.In intact specimens it is not possible to verify of the position of caudal-fin rays without clearing and staining or x-raying.Therefore, principal caudal rays were counted as the first long unbranched fin ray plus all following branched rays.In the text, these counts are represented by 8,4 or 8,3 or 7,4 (= upper-lobe fin rays and lower-lobe fin rays).Some measurements could not be taken on the holotype of Physopyxis lyra due to its fragile condition.The pectoral, anal and caudal fin-ray counts of the holotype are those found in Cope's original description.Clearing and double-staining procedures follow Taylor & Van Dyke (1985).Illustrations were made under a camera lucida attached to a stereomicroscope.Specimens of Amblydoras, a taxon closely related to Physopyxis (Higuchi, 1992), were used for anatomical and skeletal comparisons.Acronyms follow Leviton et al. (1985) with addition of UNAP (Universidad Nacional de la Amazonía Peruana).

Diagnosis.
Physopyxis can be distinguished from the other Doradidae by the miniature size (adults less than 31 mm SL) and a unique combination of additional features: extreme development of the exposed pectoral girdle; well developed coracoid process longer than the postcleithral process; anterior plate of the nuchal shield absent; dorsal spine serrated

O F S
only along the basal portion of its anterior margin; two infraorbital bones in young that become fused into a single plate in adult specimens; pectoral spine reaching to base of anal fin.Scapular girdle extremely well developed anteriorly and ventrally, forming deep groove along its anterior contour.Cleithrum laterally expanded and visible from above, sculptured with shallow grooves up to postcleithral process.Postcleithral process relatively short, its tip reaching to or slightly surpassing vertical through origin of dorsal spine.Coracoid processes very long and broad (larger than postcleithral process), with expanded distal tip.Ventral surface of coracoid process ornamented with well-defined longitudinal pattern of parallel grooves and ridges along its entire length.At posterior tip of coracoid, grooves and ridges curve

O F S
outwards following expansion of process.Dorsal and pectoral spines strongly ossified.Dorsal spine pentagonal in cross-section with longitudinal groove along each lateral side, serrate along basal portion of anterior margin, posterior margin smooth.Pectoral spine well developed, depressed and curved, its tip usually reaching anal-fin origin.Two or three grooves on both upper and lower surfaces of pectoral spine.Strong hook-like teeth present along anterior and posterior margins of pectoral spine; basal most teeth (i.e., first five) along anterior margin directed toward base of spine, more distal teeth directed toward spine tip; all teeth along posterior margin directed toward pectoral-spine base.
Vast majority of observed specimens with 26 lateral plates, each with single posteriorly directed spine.Number of lateral plates 23-27, with few juvenile specimens (less than 16.37 mm SL) from Guaporé drainage lacking plates entirely (see Table 1).Portion of lateral plate above spine and lateral line (dorsal wing) deeper than portion below (ventral wing).Lateral plates meeting dorsally in large specimens.
Dorsal-fin rays I,5.Dorsal-fin origin situated at anterior third of body.Pectoral-fin rays I,4.Pectoral fin located at vertical through branchial opening.Pelvic-fin rays 7. Pelvic fin inserted at vertical through coracoid process tip, approximately at middle of body; tip of pelvic fin slightly surpassing anal-fin origin.Anal fin moderately long, with 16 rays in total (branched and unbranched).Adipose fin small, membranous.Caudal fin truncate to slightly emarginate, with 8,4 rays.

Color in alcohol.
Body ground color tan with brown blotches and spots.Head usually more pigmented than body.Three or four dark brown irregular saddles on dorsum extending onto sides as full or partial bars: anteriormost at base of dorsal fin and usually reaching to lateral line; second from adipose fin to anal fin; third at beginning of caudal peduncle, and fourth at base of caudal fin rays.Last two bars may be joined into

P R O O F S
one that covers entire caudal peduncle.Barbels tan with brown transverse bands along its entire length.All fins similar in appearance, with dark transverse bands across rays and membranes separated by unpigmented interspaces.Dorsal and pectoral spines with unpigmented tips.Spines and rays with brown transverse bands.Ventral surface variably pigmented, light or dark, with chromatophores regularly spaced over abdomen and scapular bridge.Coloration in fresh specimens similar to above, but more conspicuous.
Distribution.Known from the rio Ampyiacu (and lowland portions of other tributaries to the upper Amazon in northeastern Peru) to the rio Uatumã, a left bank tributary to the Amazon in eastern Amazonas State, Brazil.No reliable records exist for the rio Negro basin (one specimen recorded from upper rio Negro may be incorrectly labeled) (Fig. 6).
Habitat.Physopyxis lyra is usually found in places with accumulated organic debris, like dense meshes of roots of floating macrophytes that are abundant in rivers with turbid water.Specimens also can be found Scapular girdle and cleithrum as in P. lyra.Postcleithral process relatively short, its tip reaching to or slightly surpassing vertical through dorsal-spine origin.Coracoid processes very long, slender (larger than postcleithral process), with well defined straight longitudinal grooves and ridges along its entire length.Tip of coracoid process pointed, not expanded.
Dorsal and pectoral spines very strong; ornamented, shaped and serrated as in P. lyra.
Vast majority of observed specimens has 25 lateral plates (range 23-27, plates present in all specimens).Lateral plates with single medial to submedial row of posteriorly-directed spines and at least one additional row of spines on dorsal wings (Fig. 9).Lateral plates of both sides meeting dorsally in large specimens.Dorsal and ventral sections of lateral plates usually same size; in some specimens, dorsal wing smaller.

P R O O F S
Dorsal-fin rays I,5.Dorsal-fin origin situated at the anterior third of the body.Pectoral-fin rays I,4.Pectoral fin located at vertical through branchial opening.Pelvic-fin rays 7. Pelvic fin inserted at vertical through coracoid process tip, approximately at middle of body; tip of pelvic fin lightly surpassing anal-fin origin.Anal fin with 13 rays in total.Adipose fin absent in most specimens.When present, adipose fin small, membranous.Caudal fin truncate to slightly emarginate, with 8,3 or 7,4 rays.

Color in alcohol.
Physopyxis ananas has a color pattern similar to that described for P. lyra, except that P. ananas is usually darker overall.
Distribution.Physopyxis ananas has the widest distribution among the species of the genus, occurring throughout lowlands in entire Amazon (including rio Negro) and rio Essequibo basins (Fig. 6).
Etymology.From the generic name for the pineapple, Ananas (Bromeliaceae).The specific name ananas is an allusion to stout body and spiny appearance of species due to presence of additional row(s) of spines on lateral plates.

Habitat.
As mentioned for Physopyxis lyra, P. ananas can be found in shallow waters where organic debris accumulates, such as submerged litter banks.A large number of specimens were collected along with hundreds of specimens of P. lyra among the submerged roots of aquatic macrophytes (Paspallum repens, Poaceae) at lago Amanã, rio Japurá basin.Physopyxis ananas and P. lyra also were collected together in rio Nanay (a moderate blackwater) upstream from Iquitos.

Physopyxis cristata, new species
Fig. 7 Holotype Diagnosis.Physopyxis cristata can be easily distinguished from its congeners by possessing an incomplete lateral line that ranges between five and twelve lateral plates; lateral plates weakly ossified, externally visible only by posteriorly-oriented spine; tips of neural spines exposed, perforating skin middorsally along posterior portion of body, forming a crest between dorsal and caudal fins.
Description.Morphometric data summarized in Table 3. Largest specimen examined measures 22.73 mm SL.Body slightly slender, moderately deep with greatest body depth at origin of dorsal fin (body depth 27-30% of SL).Top of head and nuchal plates roof shaped, with bony ornamentation arranged in shallow grooves concentrated along nuchal shield crest and borders.Anterior nostril tubular and placed near border of snout.Posterior nostril nearer to orbit than to snout.Snout short, its length twice orbital diameter.Lacrimal bone well developed, dorsal and ventral margins serrated with conspicuous spines.Mouth terminal.Barbels simple, long, slightly compressed, with papillae along inferior surfaces.Maxillary barbel reaching to or surpassing tip of postcleithral process.
Outer mental barbel reaching point of insertion of pectoral spine.Inner mental barbel slightly shorter than outer mental barbel.Scapular girdle as in Physopyxis lyra.Cleithrum laterally expanded and visible from above, sculptured with shallow grooves up to postcleithral process.Postcleithral process relatively short, its tip reaching to or slightly surpassing vertical through dorsal-spine origin.Coracoid process very long, slender (larger than postcleithral process), with well defined straight longitudinal grooves and ridges along its entire length.Tip of coracoid process pointed, not expanded.Dorsal and pectoral spines strongly ossified, serrated and grooved as in P. lyra.
Lateral line incomplete and asymmetric, ranging from five Color in alcohol.Physopyxis cristata has same color pattern as described for P. lyra.
Distribution.This species has been recorded only from middle portion of the rio Negro basin (Amazonas drainage), Amazonas State, Brazil.
Etymology.The name cristata, from Latin cristatus, meaning crested, in allusion to externally visible series of emergent neural spines.
Habitat.Some specimens included in type series were found in accumulated leaf litter, suggesting habitat similar to that observed in P. lyra.Dwarf cichlids of the genus Apistogramma and juvenile specimens of Amblydoras were collected with specimens of P. cristata.

Discussion
Higuchi (1992) stated that the basal condition among doradids is a well-developed pectoral girdle, with the postcleithral process much larger than the coracoid process.

P R O O F S
In Physopyxis, the cleithrum is large but the coracoid process is extremely long, strong and exposed (i.e., much larger than the postcleithral process).The coracoid process is proportionally longer in P. lyra than in P. ananas and P. cristata and shows longitudinal grooves and ridges in all three species.In P. lyra, these longitudinal grooves and ridges turn abruptly to the sides at the end of the coracoid process, following the enlargement of this extremity (see description for details).In the other two species the grooves and ridges run parallel to the longitudinal axis of the body along the entire coracoid process.Interestingly, even in juveniles of P. lyra which do not yet show the development of the distal enlargement of the coracoid process, the grooves and ridges are already directed laterally near the tip, forming little spines on the border of the bone.Coracoid process enlargement shows geographic variation.Specimens of P. lyra from the rio Guaporé, for instance, do not show the enlargement on the tip of the process, but do have the juvenile groove and ridge pattern of specimens from other drainages (i.e., grooves and ridges directed laterally near tip of coracoid process).Higuchi (1992) pointed out a unique feature of the fin rays of Physopyxis: a terminal bifurcation of the flexible fin-rays (Fig. 8) (vs.non-terminal bifurcation of rays).This feature was observed in all examined specimens of the three species.Fin-ray counts show a great deal of variation, especially for anal and caudal fins (Tables 1-3).Distal bifurcation in flexible fin-rays may cause miscounts due to difficulty in correctly interpreting the limits between branched and unbranched rays.The caudal fin in Physopyxis also is distinctive.The primitive condition for Siluriformes is the presence of nine principal caudal-fin rays (i.e., rays articulating with parhypural and hypurals only) on both upper and lower lobe.However, most catfish groups, including doradids, exhibit more principal rays on the lower lobe (e.g., 7+8, 7+9, 8+9, etc.) (Lundberg & Baskin, 1969).Physopyxis differs by having fewer principal rays in the lower caudal fin lobe than in the upper lobe.In most cases there are eight principal rays on the upper lobe and only four on the lower lobe (Fig. 8).
The most plastic feature in Physopyxis is the lateral plate complex, varying from a complete lateral line covered by welldeveloped plates, running along the entire body (e.g., most adult P. lyra and P. ananas), to an incomplete lateral line, with small and poorly ossified plates (e.g., adult P. cristata).Few doradids show lateral plate reduction or interruption (e.g., Hassar, Nemadoras leporhinus, Doraops, Kalyptodoras, and Wertheimeria, sensu Sabaj, 2002).However, the only doradid previously reported to have an incomplete lateral line is an undescribed genus and species related to Amblydoras (Higuchi, 1992;Britski et al., 1999).The lateral plate pattern found in Physopyxis cristata is similar to the one found in Higuchi's undescribed taxon.In Higuchi's cladistic analysis of the family, a clade formed by Amblydoras and Higuchi's undescribed genus is the sister group of Physopyxis.A more complete phylogenetic study is needed to clarify the level of homology of lateral line reduction among doradids.
In Physopyxis lyra and P. ananas (species with complete lateral lines), there is substantial size-related variation in the degree of development, ossification and ornamentation of the lateral plates.Young specimens have undeveloped plates that do not meet dorsally.Increase in body size is accompanied by plate development until complete middorsal contact is made between the plates on both sides of the body.The direction of plate development is cephalo-caudal, whereby the posterior plates are the last ones to develop completely and contact dorsally.In Physopyxis ananas, an additional

O F S
row of plate spines is formed early in development and becomes larger and more conspicuous with age.This kind of development generally is not seen in other spiny catfishes (e.g., Loricariidae), in which the young exhibit large spines that become less conspicuous with increased size.The number of additional spines and the body size at which full spine development is attained vary with locality or drainage.Similar size specimens from different locations may exhibit distinct stages of plate ornamentation.The variation in plate ornamentation found in specimens of P. ananas can be seen in Fig. 9. Lateral plate ornamentation in P. lyra also may vary with drainage.Specimens from the rio Uatumã have the posterior border of the lateral plates serrated, mainly dorsally.Specimens from the rio Guaporé may have an incomplete lateral line but exhibit all other diagnostic features of P. lyra.In a group of 38 specimens from this drainage, 21 have 24 lateral plates or less, and four small specimens (12.62-16.37mm SL) are apparently naked.One of these specimens has an inconspicuous ossification along the lateral line, suggesting an early stage in plate development.
Physopyxis cristata is the only doradid known to have an externally visible extension of the neural spines on pre-caudal and caudal vertebrae (see description for more details).Higuchi (1992) cited as an autapomorphy for P. lyra, monotypic at that time, the presence of flattened and enlarged neural and hemal spines.Physopyxis ananas has the same feature.Physopyxis cristata, however, has the slender condition of neural and hemal spines that is found in other doradids (Fig. 8).
Physopyxis also is characterized by the lack of an anterior nuchal plate.Higuchi (1992) noted that the anterior nuchal plate might be fused to the middle nuchal plate, based on the typical shapes of these plates in other doradids.This character was first noticed in some Auchenipteridae by Ferraris (1988), and might be homoplastic within Doradoidea.In the Doradidae, some taxa of Doradini have the anterior nuchal plate greatly reduced, grain shaped (Higuchi, 1992: 122, character 84).This is clearly not homologous to the condition presented in Physopyxis, in which the anterior nuchal plate appears fused to the middle nuchal plate.
The large sample of Physopyxis examined resulted in the expansion of the geographic distribuition of the genus and the recognition of intra and interespecific variation.However, intrageneric and intrafamilial phylogenetic relationships remain largely unresolved.
Physopyxis lyra differs from the other species of the genus by possessing a single row of spines on the lateral plates and a strong scapular girdle with long, broad coracoid processes having distal tips enlarged and divergent.
Physopyxis lyra; c.Physopyxis ananas; d. ventral view of scapular girdle in P. ananas and P. cristata; e. ventral view of scapular girdle in P. lyra.Diagnosis.Snout short, its length twice orbital diameter.Lacrimal bone well developed, dorsal and ventral margins serrated with conspicuous spines.Mouth terminal.Barbels simple, long, covered with papillae along inferior surfaces.Maxillary barbel reaching to or surpassing tip of postcleithral process.Outer mental barbel reaching point of insertion of pectoral spine.Inner mental barbel shorter, approximately two thirds of length of outer mental barbel.