Microlepidogaster dimorpha, Martins & Langeani, 2011

Martins, Fernanda de Oliveira & Langeani, Francisco, 2011, Microlepidogaster dimorpha, a new species of Hypoptopomatinae (Siluriformes: Loricariidae) from the upper rio Paraná system, Neotropical Ichthyology 9 (1), pp. 79-86 : 80-83

Microlepidogaster dimorpha , new species Figs. 1, 2b, and 3

Holotype. DZSJRP 10543, 37.6 mm SL, female, Brazil , Minas Gerais , Uberaba , riacho Grotão at Fazenda Nossa Senhora da Abadia, unpaved road at BR-262, rio Grande drainage, 19º41’31”S 47º 42 ’ 57 ”W, 12 May 2007, L. G. G. Silveira & F. Langeani .

Paratypes. All from Brazil , Minas Gerais , rio Grande drainage, Uberaba. DZSJRP 5564, 11, 25.8-35.1 mm SL (10, 25.8-35.1 mm SL), road Uberaba-Almeida Campos and Nova Ponte, rio Uberaba, 19º39’40”S 47º49’23”W , 21 May 2003, J. P. Serra, F. Langeani, F. R. Carvalho & D. O. Tavares; DZSJRP 8750, 19, 2 c&s, 19.8-37.7 mm SL (14, 25.0- 37.7 mm SL), MCP 45866, 2, 26.7-30.8 mm SL, MNRJ 37848, 2, 25.5-26.8 mm SL, MZUSP 107585, 2, 27.8-30.2 mm SL, same locality of holotype, 8 Sep 2006, F. Langeani, F. R. Carvalho, C. P. Ferreira, H. F. Chaves & F. O. Martin; DZSJRP 12332, 17, 2 c&s, 20.3-34.1 mm SL (6, 29.7-37.6 mm SL), LBP 4854, 4, 29.8-32.9 mm SL, MCP 41912, 4, 28.7-34.0 mm SL, collected with holotype.

Diagnosis. Microlepidogaster dimorpha differs from M. perforatus ( Tables 3 and 4) and M. longicolla Calegari & Reis, 2010 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 having the iris operculum (vs. absent); 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); 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% in SL vs. 13.4-16.2% in M. longicolla ).

Description. Morphometric and meristic data are given in Tables 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. 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

(DZSJRP 5564, 8750,12332; MCP 45866;MNRJ 37848; MZUSP

107585); range includes holotype. SD = Standard deviation.

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.

Lips roundish, papillose; lower lip larger than upper lip; larger papillae near oral opening. Maxillary barbel reduced, free from oral disk. Teeth slender, bifid; median cusp larger and rounded, lateral smaller and pointed. Premaxillary teeth 15-28 (mode = 23,24). Dentary teeth 12-25 (mode = 21). Premaxillary and dentary accessory teeth absent.

Dorsal fin ii, 6-7 (mode = 7), originating approximately at vertical through end of pelvic-fin base; its length surpassing anal-fin origin; spinelet small, somewhat rectangular, anterior and posterior margins slightly straight; locking mechanism non-functional. Anterior portion of compound supraneuralfirst dorsal-fin proximal radial contacting neural spine of 7 th vertebra; posteriorly contacting the 8 th vertebra. Pectoral fin i, 6-7 (mode = 6); originating immediately behind opercular opening and surpassing pelvic-fin origin. Cleithrum and coracoid exposed and supporting odontodes laterally, covered by skin medially. Arrector fossae partially enclosed by ventral lamina of coracoid; opening extending laterally approximately halfway towards pectoral-fin base. Pectoral axillary slit present, about 2.5 times in orbital diameter. Pelvic fin i, 5-6 (mode = 5); reaching anal-fin origin in males when depressed. Anal fin i, 4-6 (mode = 5); originating at vertical through end of dorsal-fin base. Caudal fin i, 14, i; lobes equal in size; 5-6 (mode = 5) dorsal and 4-5 (mode = 5) ventral procurrent rays.Adipose fin and azygous plates absent. Median lateral plate series 24-27 plates, complete from compound pterotic to caudal-fin base. Vertebrae 29-30 (mode = 29).

Color in alcohol. Most specimens with a dark brown color along the dorsal portion of head and dorsal midline of body. Four dorsal dark saddles, not extending laterally, inconspicuous in adults. Longitudinal clear stripe from dorsal portion of snout to nostril. Lateroventral portion of head unpigmented. Lateral portion of body brown; an inconspicuous dark longitudinal stripe at median plate series, extending from compound pterotic to vertical through end of depressed dorsal fin. Ventral surface of body light brown. Dorsal, anal, pectoral, and pelvic-fins membrane hyaline; all rays with transverse dark bands. Caudal fin mostly dark brown, except for hyaline portions at lobe tips, middle-rays extremities, and a circular area in the middle of each lobe.

Sexual dimorphism. Males with a conspicuous urogenital papillae immediately posterior to anus (vs. absent in females); expanded flap of skin on dorsal surface of the first pelvic-fin ray and branched rays, less developed in the latter (vs. absent 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 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.