Microlepidogaster longicolla, Calegari & Reis, 2010

Calegari, Bárbara B. & Reis, Roberto E., 2010, A new species of Microlepidogaster (Siluriformes: Loricariidae: Hypoptopomatinae) from the upper rio Paraná basin, Brazil, Neotropical Ichthyology 8 (3), pp. 625-630 : 626-629

Microlepidogaster longicolla , new species Fig. 1

Holotype. MCP 44877, female, 39.8 mm SL, Brazil, Distrito Federal, Brasília, ribeirão Santana, tributary to rio São João , on road from Cidade Ocidental to Brasília , 16°00’55”S 47°48’02”W, 13 Jul 1998, R. E. Reis, L. R. Malabarba, E. H. L. Pereira & J. P. Silva.

Paratypes. All from Brazil. AMNH 251432 , 5 , 23.5-35.7 mm SL, DZSJRP 12453 , 5 , 39.7-44.5 mm SL, MCP 23323, 13 , 18.5 - 42.2

mm SL, 5 c&s, 37.7-42.5 mm SL, same locality as holotype. LISDEBE 2662, 3, 33.3-36.8 mm SL, Distrito Federal, Brasília, córrego Taquara at mouth of córrego Onça , Ecological Reserve of the Instituto Brasileiro de Geografia e Estatística - IBGE, 15°56’22”S 47°53’53”W, 31 Jan 1985, M. Ribeiro, E. C. Lopes & F. Paixão. MCP 23322, 10 , 18.1-36.5 mm SL, Goiás, Cidade Occidental , creek near Mesquita , on road from Cidade Ocidental to Brasília , 16°55’04”S 47°51’15”W, 13 Jul 1998, R. E. Reis, L. R. Malabarba, E. H. L. Pereira & J. P. Silva. MCP 23324, 1 , 38.3 mm SL, Distrito Federal, Brasília, creek on highway BR-020 between road BR-251 and Planaltina, 15°44’29”S 47°39’48”W, 13 Jul 1998, R. E. Reis, L. R. Malabarba, E. H. L. Pereira & J. P. Silva. MCP 23325, 12 , 19.3-41.2 mm SL, 3 c&s, 27.6-41.6 mm SL, Distrito Federal, Planaltina, ribeirão Mestre D’armas in Planaltina, 15°36’25”S 47°41’31”W, 13 Jul 1998, R. E. Reis, L. R. Malabarba, E. H. L. Pereira & J. P. Silva .

Diagnosis. Microlepidogaster longicolla is readily distinguished from the only other species of Microlepidogaster , M. perforatus , by having a continuous lateral line (vs. the lateral line discontinuous, with a gap between the anterior and posterior lateral line segments; Fig. 2 ), the median lateral plate series reaching the end of the caudal peduncle (vs. median lateral plate series terminating two plates before the end of the caudal peduncle; Fig. 2 ), the shorter pectoral-fin spine (13.4-16.2 vs. 18.2-21.0% SL), a smaller interorbital distance (38.9-43.1 vs. 47.7-53.3% HL), more numerous dentary teeth (16-29 vs. 12-15), the anterior margin of the snout naked (vs. the snout completely covered by plates), the preopercle not contacting the fourth postrostral plate (vs. the preopercle contacting and extending to midlength of that plate), the absence of the anterior processes of the supraneural (vs. supraneural bearing a bilateral pair of processes along its anterior margin), and the dorsal fin located more posteriorly relative to the parietosupraoccipital, where the neural spine of the tenth or eleventh vertebral centrum supports the compound supraneural plus first pterygiophore of the dorsal fin (vs. compound supraneural plus first pterygiophore supported by the neural spine of the eighth or ninth vertebra; Fig. 3 ).

Description. Proportional measurements and counts given in Tables 1 and 2, respectively. Dorsal body profile slightly arched from snout tip to posterior margin of frontal bone. Parieto-supraoccipital slightly elevated and convex. Profile of the posterior region of parieto-supraoccipital and first predorsal plates slightly concave.Almost straight and slightly ascending from that point to dorsal-fin origin. Slightly concave and postero-ventrally oriented along dorsal-fin base, straight from terminus of dorsal-fin base to end of caudal peduncle and angling upward slightly immediately before caudal-fin origin. Greatest body depth located at dorsal-fin origin. Least body depth situated at posterior portion of caudal peduncle. Greatest body width along opercular and cleithral regions. Body progressively narrowing caudally from cleithrum. Ventral and especially dorsal surface of caudal peduncle transversely flattened, with caudal peduncle somewhat square in cross section.

Head and snout broad, snout rounded in dorsal view. Region of prenasal plates between nostrils protuberant, bordered by elongate and shallow depressions extending from each nostril to near snout tip. Dorsal margin of orbit slightly elevated, interorbital region almost flat. Eye small, dorsolaterally positioned. Compound pterotic completely perforate with middle to large size fenestrae; larger fenestrae anteroventral margin.

Body surface without well-developed keels. Five or six (often six) transverse rows of predorsal plates, including nuchal plate. Lateral line continuous, with median lateral plate series formed by 27-30 plates. Odontodes on head and trunk pointed, uniform in size and distribution. Body entirely covered by plates, except region around anus, region overlying lateral opening of swimbladder capsule, depression from nostril to rostral plates, area between pectoral girdle and lower lip, and area around bases of paired fins. Abdominal region entirely covered with small platelets. Lateral abdominal plates absent.Ventral portions of cleithrum and coracoid exposed and supporting odontodes laterally, covered with skin and median abdominal plates medially. Lips rounded and papillose. Lower lip falling short of line between ventral tips of contralateral canal-bearing lateral cheek plates. Teeth slender, bifid, with blade-like larger medial cusp and smaller lateral cusp.

Dorsal-fin II,7, its origin located at vertical running close to posterior rim of anus. Dorsal fin located distinctly posterior of parieto-supraoccipital. Neural spine of tenth (3 c&s specimens) or eleventh (2 c&s specimens) vertebra ( Fig. 3 ) supporting compound supraneural plus first dorsal-fin proximal radial. Supraneural without pair of processes along anterior margin. Spinelet reduced and plate-like, and dorsalfin locking mechanism non functional. Adipose fin absent. Pectoral fin I,6, with posterior fin margin slightly rounded. Tip of depressed pectoral fin extending one-third of pelvicfin length. Axillary slit of pectoral fin absent. Pelvic fin i,5, short, with robust thickened first ray. Tip of adpressed fin extending to point midway between anus and anal-fin origin in females. Reaching to or beyond anal-fin origin in males. Adult males with fleshy flap along posterodorsal margin of thickened first pelvic-fin ray. Anal fin i,5. Caudal fin i,14,i.

Color in alcohol. Ground color of dorsal surface of head and body light to median brown; pale yellowish, mostly unpigmented ventrally. Longitudinal dark brown stripe present on lateral surface of head and body. Stripe begins laterally on snout tip and extends to end of caudal peduncle. Four inconspicuous darker saddles on dorsal surface of body. First saddle at dorsal-fin origin, second behind dorsal-fin base, third and fourth between dorsal and caudal fins. Head with two light stripes from snout tip to nares. Dorsal margin of orbital with creamy white light stripes, extending to posterodorsal margin of compound pterotic and then along middorsal series of lateral plates to around middle of dorsalfin base. Parieto-supraoccipital with two creamy stripes, diverging and prolonged along predorsal plates to end of dorsal-fin base. Ventrolateral margin of head from upper lip to opercle and pectoral-fin insertion creamy white, and strongly contrasting with longitudinal dark brown stripe. Ventral surface from lips to anterior margin of cleithrum and abdominal region mostly unpigmented. Caudal peduncle with scattered dark chromatophores. All fins mostly hyaline with chromatophores forming scattered spots most conspicuous on unbranched rays; dorsal-fin base more densely pigmented. Caudal fin uniformly dark-brown, except for distal tips of upper rays sometimes with small hyaline area.

Sexual dimorphism. Secondary sexual dimorphism in Microlepidogaster longicolla is most obvious in the conical urogenital papilla, which is positioned just behind the anal opening in males; absent in females.Adult males also possess a fleshy flap along the dorsal margin of first thickened pelvicfin ray that is absent in females. Males have a longer pelvicfin extending to the anal-fin origin, whereas the pelvic fin never reaches that point in females. The first thickened pelvicfin ray is strongly arched in female; but straight in males.

Distribution. Microlepidogaster longicolla is known from five localitiesintheupperreachesoftherioSãoBartolomeu, atributary to the rio Corumbá, itself a tributary to the rio Paranaíba of the upper rio Paraná basin near Brasília, in central Brazil ( Fig. 4 ).

Etymology. The species epithet, longicolla , is from the Latin longus, long and collum, neck, meaning long-necked in allusion to the long predorsal region resulting from the posterior shift of the dorsal fin. An adjective.

Figures

Fig. 1. Microlepidogaster longicolla, holotype, MCP 44877, female, 39.8 mm SL. Brazil, Distrito Federal, Brasília, ribeirão Santana, tributary to rio São João, on road from Cidade Ocidental to Brasília.

Fig. 2. Lateral plates of species of Microlepidogaster. a) Microlepidogaster longicolla, MCP 23323; b) M. perforatus, MCP 17717. Scale bar = 5 mm.

Fig. 3. Dorsal-fin skeleton of Microlepidogaster. a) Microlepidogaster longicolla, MCP 23323; b) M. perforatus, MCP 17717. DSP = dorsal-fin spinelet; NP = nuchal plate; PT2 = second dorsal-fin pterygiophore; SN+PT1 = fused supraneural and first dorsal-fin pterygiophore; VI-X = vertebrae VIth to Xth. Scale bar = 2 mm.

Fig. 4. Map of southeastern Brazil showing the distribution of Microlepidogaster longicolla (circles) and M. perforatus (square). T = type-locality. Each symbol may represent more than one locality.