Hisonotus prata, Carvalho & Reis, 2011

Carvalho, Tiago Pinto & Reis, Roberto E., 2011, Taxonomic review of Hisonotus Eigenmann & Eigenmann (Siluriformes: Loricariidae: Hypoptopomatinae) from the laguna dos Patos system, southern Brazil, Neotropical Ichthyology 9 (1), pp. 1-48 : 30-33

Hisonotus prata , new species

Figs. 4e, 8e, 27b, 33, 34, and 35

Hisonotus sp. 1 . -Reis & Carvalho, 2007: 84 [listed].

Holotype. MCP 44513, 31.8 mm SL, female, Brazil, Rio Grande do Sul, Nova Prata, rio da Prata on Passo do Despraiado, 28º38’01”S 51º36’51”W, 24 Oct 2006, T. P. Carvalho & V. A. Bertaco.

Paratypes. All from Brazil, Rio Grande do Sul, rio da Prata drainage, ANSP 188703 , 3 , 25.6 - 32.0 mm SL; MCP 40492, 18 , 19.5-33.2 mm SL; MZUSP 104945 , 3 , 28.3 mm SL; collected with the holotype. MCP 22204, 9 + 3 c&s, 14.3-29.3 mm SL, collected at type locality, 20 Jan 2006, R . E. Reis, J. F. P. Silva & E. H. L. Pereira.

Diagnosis. Hisonotus prata differs from its congeners, except H. carreiro , H. francirochai , H. iota , and H. leucophris by the presence of a conspicuous tuft of enlarged odontodes on the tip of the parieto-supraoccipital ( Fig. 34), vs. odontodes on the tip of parieto-supraoccipital similar in size, not enlarged or only slightly larger over the remaining odontodes on the parieto-supraoccipital. It differs from H. francirochai , H. iota , and H. leucophrys by having the anterior portion of snout with an odontode-free band ( Fig. 35), vs. snout complete covered with odontodes, without an anterior band free of odontodes. Hisonotus prata can be distinguished from H. carreiro by having a shorter dorsal-fin spine 22.6- 25.5% SL, mean 24.5%, vs. 24.3-29.0% SL, mean 26.6% ( Fig. 30); shorter pectoral-fin spine 22.0-25.6% SL, mean 24.0 %, vs. 24.7-29.0% SL, mean 26.7%. ( Fig. 31); and by its general color pattern of dorsal surface of body which is dark green in life specimens and dark gray to dark brown in alcohol preserved specimens, vs. a yellowish pattern in life, pale yellow to light brown coloration in alcohol preserved specimens.

Description. Morphometrics and meristics in Table 9. Adult size small for members of this genus (maximum size 33.2 mm in the SL). Body stocky, robust, without conspicuous keels. Caudal peduncle round in cross section. Dorsal profile convex from tip of snout to nares to parieto-supraoccipital, convex bump at parieto-supraoccipital tip, almost straight and posterodorsally inclined from that point to dorsal-fin origin. Dorsal-fin base straight and posteroventrally sloped, almost straight from posterior end of dorsal-fin base to caudal-fin origin. Ventral profile almost straight from snout tip to anal-fin origin, concave from that point to caudal-fin origin. Greatest body depth at dorsal-fin origin. Least body depth at middle of caudal peduncle. Posterior profile of caudal fin slightly concave. Head and snout broad, snout rounded in dorsal view, body progressively narrowing posterior to pelvic-fin insertion. Snout region anterior to nares concave, interorbital region convex. Upper margin of orbit not elevated. Eye dorsolaterally positioned. Iris operculum present.

Pectoral fin I,6. Pectoral-fin posterior margin slightly rounded; when depressed tip extending anterior to middle of pelvic fin. Posterior margin of pectoral-fin spine smooth in adults, juveniles with serrae along distal third of pectoral-fin spine. Pectoral-fin axillary slit present, located below posterior bony margin of cleithral process. Pelvic fin i,5. Tip of depressed fin just reaching anal-fin origin in females, but extending beyond that point in males. Dorsal II,7. Dorsal-fin origin located slightly posterior to vertical through pelvic-fin origin. Dorsal-fin spinelet present, laterally extended. Anal fin i,5. First anal-fin pterygiophore exposed anterior to anal fin. Adipose fin absent. Caudal fin i,14,i.

Body almost entirely covered by plates except for region overlying opening of swim bladder capsule, area between pectoral girdle and lower lip, region around anus, and area around base of paired fins. Rostral plate with posterior notch articulation with mesethmoid. Rostral plate thickened, with an odontode-free band between dorsad and ventrad series of odontodes ( Fig. 35). Snout plates anterior to nares reduced, small unplated area between rostral plate and nostril. Two or three rows of predorsal plates (rarely two). Lateral line incomplete, with gap without pores along middle length of body, posterior portion of lateral line sometimes absent. Median plate series truncated, not reaching posterior end of caudal peduncle ( Fig. 4e). Abdominal plates arranged in three rows anteriorly and irregularly arranged between pelvic-fin insertions. Lateral abdominal plates slightly larger and forming regular series. Median abdominal series usually formed by one plate row. Naked area between lateral and median abdominal plate series in most specimens ( Fig. 8e). Coracoid and cleithrum exposed and covered by odontodes, except for median region of cleithrum between arrector fossae openings and medial region of coracoids.

Odontodes on parieto-supraoccipital tip greatly enlarged, raised odontodes arranged in rounded patch, approximately five times larger than those of surrounding areas ( Fig. 34). Head, fin-spines, and body plates covered with odontodes, larger on anterior surface of all fin spines, and on ventral and dorsal margin of rostrum. Odontodes medially directed on pelvic-fin thickened unbranched ray. Anteroventral margin of compound pterotic with median-to-large size perforations. Infraorbital canal entering infraorbital series via sphenotic. Lips roundish and papillose, posterior margin of lower lip fimbriate. Maxillary barbel present.

Premaxillary and dentary teeth slender proximally and flattened distally; bifid, major (medial) cusp large and rounded, minor (lateral) minute pointed ( Fig. 27b). Accessory patch of teeth absent on dentary and premaxilla.

Compound ventral hypural plate (hypurals 1-2) and compound dorsal hypural plate (hypurals 3-5) completely fused to each other. Total vertebrae 28 (2 c&s).

Color in alcohol. Ground color of dorsal and lateral surfaces dark gray. Dorsal and lateral body surfaces with round dark gray spots. Dorsal and lateral portions of head darker than body, except for lighter cheek region. Ventral surface of body pale yellow, except for scattered chromatophores, these forming spots on ventral surface of caudal peduncle. Region anterior to nares lighter than surrounding areas, but not forming longitudinal light stripes beyond this point. Parietosupraoccipital tip lighter than remaining dorsal surface. Paired, anal, and dorsal fins mostly gray pigmented, with light transverse bands, forming striped pattern. Caudal fin almost completely, except for pair of round to somewhat triangular hyaline areas in middle portion of upper and lower lobes. Unbranched rays of caudal fin with striped pattern of transverse light bands. Ground color in life dark green.

Sexual dimorphism. Urogenital papilla, positioned just behind the anal opening in males. Adult males also possess a developed fleshy flap along the dorsal margin of first thickened pelvic-fin ray, that is absent in females. Flap slightly wider basally and progressively narrowing distally. In juvenile males, flap smaller or absent. Males have a longer thickened pelvic-fin unbranched ray that extends beyond anal-fin origin, with pelvic-fin ray reaching just to anal-fin origin in females.

Distribution and habitat. Hisonotus prata is endemic to the rio da Prata, tributary of rio das Antas, in the rio Taquari drainage, which is a tributary of the rio Jacuí basin in the laguna dos Patos system ( Fig. 32). The rio da Prata, at the type locality, is a rapid flow watercourse, wide and shallow, with an average depth of 0.5 m, shallower in most of its extension, with clear water, rocky bottom and great amounts of submersed vegetation ( Fig. 10b). The specimens were caught between aquatic vegetation, individuals being associated with plants of the genus Echinodorus , which form green islands in the faults of the rocky substrate. Hisonotus prata is collected in the vegetation with the undescribed Hypoptopomatinae Eurycheilichthys sp. 2 .

Etymology. The specific epithet, prata , refers to rio da Prata, the river basin where this species is known. It is treated as a noun in apposition.