Microlepidogaster dimorpha, a new species of Hypoptopomatinae (Siluriformes: Loricariidae) from the upper rio Paraná system

Microlepidogaster dimorpha, new species, is described from tributaries of rio Grande, upper rio Paraná system. Microlepidogaster dimorpha differs from M. perforatus and M. longicolla by having first dorsal-fin proximal radial attached to the neural spine of seventh vertebra, with posterior portion contacting also the eighth centrum (vs. first dorsal-fin proximal radial attached to the neural spine of eighth or ninth vertebra in M. perforatus, and to the neural spine of tenth or eleventh vertebra in M. longicolla); 29-30 vertebrae (vs. 31 in M. perforatus and 31-33 in M. longicolla); 18-21 mid-dorsal plates (vs. 9-13 in M. perforatus, and 13-17 in M. longicolla); deeper caudal peduncle (10.0-11.4% in SL vs. 7.7-8.5% in M. perforatus, and 5.4-7.3% in M. longicolla); greater distance between dorsal-fin origin and anal-fin insertion (19.4-23.8% in SL vs. 16.4-18.8% in M. perforatus, and 14.7-16.2% in M. longicolla); and nostril width markedly wider in males than in females (vs. approximately equivalent in size for both sexes, slightly wider in males than in females in M. perforatus, and equivalent in size for both sexes in M. longicolla). Microlepidogaster dimorpha also differs from M. perforatus by presence of the iris operculum (vs. absence); median plate series complete to caudal peduncle end (vs. median plate series truncated, with last two plates of dorsal and ventral series contacting in midline); greater head depth (43.4-53.1% vs. 40.7-42.3% in HL); greater orbital diameter (13.6-18.5% vs. 11.1-13.5% in HL); pelvic-fin first unbranched ray longer in males than in females (vs. equivalent in size in both sexes); and supraneural without paired anterior processes (vs. processes present). Additionally, M. dimorpha can be distinguished from M. longicolla by having anterior margin of snout with a paired rostral plate (vs. snout with small plates, naked in the anterior margin); by pectoral-fin axillary slit present, even in adult specimens (vs. pectoral-fin axillary slit present only in juvenile specimens); longer pectoral-fin unbranched ray (20.0-23.8% vs. 13.4-16.2% in SL in M. longicolla).


Introduction
Microlepidogaster, type species Microlepidogaster perforatus, was described by Eigenmann & Eigenmann (1889) as related to Otocinclus Cope, differing from that by having the ventral surface of body covered with minute granular plates, dorsal fin inserted far posterior to the ventrals, and temporal plate perforate.However, these characters are not unequivocal to diagnose Microlepidogaster from other hypoptopomatines, and in consequence, additional species were described inside the genus, as well as transferred from other Hypoptopomatinae genera to Microlepidogaster.
Phylogenetic analyses performed by Schaefer (1991Schaefer ( , 1997Schaefer ( , 1998) allowed a reevaluation and rearrangement of the generic composition of the Hypoptopomatinae.As a consequence, Schaefer (1998) restricted Microlepidogaster to its type species, M. perforatus, diagnosing it by the following autapomorphies: levator crest absent from the hyomandibula; dorsal fin position shifted posteriorly (first dorsal-fin proximal radial attached to the neural spine of ninth vertebra); supraneural with paired anterior processes; median plate series truncated; a median rostral plate present.
During samplings in the upper rio Paraná system, a new Microlepidogaster was collected in headwaters of the rio Grande.This contribution aims to describe this new species, based on the possession of some of the derived traits proposed by Schaefer (1998).We also make comments about the current diagnosis for the genus, and describe a sexual dimorphism never reported to Hypoptopomatinae.

Material and Methods
Measurements were made with digital calipers, point-topoint, on the left side of the specimens and to the nearest 0.1 mm, following Boeseman (1968), with modifications of Armbruster & Page (1996), and Ribeiro et al. (2005).Additional measurements were included: prepectoral length (from snout tip to pectoral-fin origin); prepelvic length (from snout tip to pelvic-fin origin); head width (width in opercle region); dorsal to anal-fin length (from dorsal-fin origin to anal-fin origin); prenasal length (from snout tip to anterior edge of nostril); internasal length (distance between inner edges); nostril width (from outer to inner edge); suborbital depth (from inferior edge of eye to ventral margin of head).Plate counts and nomenclature followed Schaefer (1997).Plates were counted from both sides in cleared and stained (c&s) specimens, prepared according to Taylor & van Dyke (1985).Vertebrae counts included five from the Weberian apparatus, and the compound caudal centrum was counted as a single element.Dorsal-fin ray counts included spinelet as first unbranched ray.Morphometric data were expressed as percents of standard length (SL), except for measurements of the head, which were given as percents of head length (HL).Sex determination was made upon dissection of mature specimens.Museum abbreviations for specimens examined are listed in Fricke & Eschmeyer (2010), with the addition of the fish collection of the Museu de Zoologia, Universidade Estadual de Londrina, Paraná State, Brazil (MZUEL).

Microlepidogaster dimorpha, new species
Figs. Diagnosis.Microlepidogaster dimorpha differs from M. perforatus (Tables 3 and 4) and M. longicolla Calegari & Reis, 2010   Greatest body width at opercular region, gradually tapering toward snout and caudal fin.Head profile rounded in dorsal view; rostral margins with thin plates, not deflected ventrally; anterior tip of rostrum with a median pair of plates; odontodes at anterior margin of snout small and leaf-shaped (Fig. 2b), some with edge slightly rounded.Odontodes equal in size and uniformly distributed, not forming rows, on head and body.Eyes small, dorsolaterally placed, not visible from ventral view.Iris operculum present.Infraorbital canal entering infraorbital series via compound pterotic.
Compound pterotic roughly quadrangular in shape, without elongate posterior extension; small to median roundish perforations on posteroventral margin.Caudal peduncle slightly flattened dorsally and ventrally, somewhat rectangular in transverse section.Abdomen partially covered by small plates, approximately same size of pupil, irregularly arranged.Body entirely covered with bone plates, except on ventral part of head, region overlying opening of swim bladder capsule, and around anus and pelvic-fin origin.
associated with skin of the anterior portion of anterior nostril (vs.absent in females; Fig. 3).
Distribution.The species is known from rio Uberaba and riacho Grotão, both tributaries of the rio Grande, upper rio Paraná system, Minas Gerais, Brazil (Fig. 4).
Etymology.Epithet dimorpha from the Greek di, two, double, and morphe, form, in allusion to the accentuated sexual dimorphism presented by the species.A feminine adjective.
Recently, a new species was proposed, M. longicolla Calegari & Reis, 2010, which was included in the Microlepidogaster by sharing with M. perforatus the dorsal fin placed posteriorly, with the first pterygiophore articulating with the neural spine of the tenth or eleventh vertebral centrum (with the eighth or ninth in M. perforatus).Now, Microlepidogaster dimorpha was included in the genus by sharing with M. perforatus two other apomorphic character states of Schaefer (1998): levator crest extremely reduced in size and median rostral plate paired.Schaefer (1998) considered the levator crest absent in M. perforatus; however Calegari & Reis (2010) identified a low crest in that species.Indeed, M. perforatus presents an extremely reduced crest in the hyomandibula, which is shared with M. dimorpha (vs.more developed in M. longicolla, as in the plesiomorphic state).
The anterior portion of the first dorsal-fin proximal radial in M. perforatus contacts the neural spine of the eighth (our analysis and Calegari & Reis, 2010) or ninth vertebrae (Schaefer, 1998).In M. dimorpha, the first dorsal-fin proximal radial contacts the neural spine of the seventh vertebra, but also the dorsal portion of the eighth, and in M. longicolla the first dorsal-fin proximal radial contacts the neural spine of the tenth or eleventh vertebra.The dorsal fin shifted posteriorly relative to the parieto-supra-occipital, however, is not exclusive for M. perforatus and M. longicolla, being also present in the species of Epactionotus Reis & Schaefer, 1998 (eighth vertebra), Parotocinclus jumbo Britski & Garavello,   2002 (eighth, Bárbara Calegari, pers. commun.),and Rhinolekos britskii (ninth), R. garavelloi, and R. schaeferi (tenth) (Martins & Langeani, 2011).Therefore, the posterior insertion of the dorsal fin is likely to have appeared independently several times within hypoptopomatines.In consequence, we think this feature deserves a more exhaustive analysis in order to understand its occurrence within the Hypoptopomatinae.
Microlepidogaster perforatus possesses two other autapomorphies absent in M. dimorpha and M. longicolla: the supraneural with a paired anterior processes, and the median plate series truncated posteriorly, with the absence of the last one or two plates of the median series, such that the last one or two plates of the dorsal and ventral series contact each other in the midline.
Furthermore, in M. perforatus and M. dimorpha the most anterior plates limiting the snout, mainly the median paired rostral plate (absent in M. longicolla), bear peculiar small rounded leaf-shaped odontodes, sometimes with a slight median projection (Fig. 2a-b).These odontodes are very different from the spine-like ones present in other members of the subfamily (Fig. 2c-f), and are proposed here as an additional diagnostic character for M. perforatus and M. dimorpha.Very similar leafshaped odontodes are also present in Parotocinclus jumbo Britski & Garavello, referred by the authors as heart-shaped odontodes (Britski & Garavello, 2002;fig. 3).
specimens); longer pectoral-fin unbranched ray.Description.Morphometric and meristic data are given inTables 1-2.Dorsal body profile convex from tip of snout to dorsal-fin origin; descending posteriorly at dorsal-fin base; almost straight from end of dorsal-fin base to caudal-fin origin.Ventral body profile almost straight; ascending posteriorly from anus to end of anal-fin base; straight to caudal-fin origin.Greatest body depth at dorsal-fin origin.
in females); pelvic fin reaching anal-fin origin, its first unbranched ray 18.3-20.9% in SL (vs.pelvic fin not reaching anal-fin origin, its first unbranched ray 15.4-18.2% in SL in females); males, usually with fewer teeth than females, probably related with their smaller size; males with wider nostril width (11.5-15.4% of HL vs. 7.9-10.3% in females), with an anterior single row of 4 to 6 small odontodes