Hisonotus heterogaster, 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 : 40-43

Hisonotus heterogaster , new species

Figs. 4h, 8h, 42, and 43

Paratypes. All from Brazil, Rio Grande do Sul, rio Jacuí drainage : ANSP 188706 , 3 , 37.1-40.7 mm SL ; MCP 41073, 5 + 2 c&s, 37.4- 44.3 mm SL ; MZUSP 104948 , 3 , 40.8-41.3 mm SL; collected with the holotype . MCP 26802, 1 , 43.0 mm SL, collected at type locality, 28 Nov 2000 , L. R. Malabarba , V. A. Bertaco, M. A. Azevedo, J . R. H. Bastos & C. Ricken .

Diagnosis. Hisonotus heterogaster differs from its congeners, except from H. aky , H. brunneus , H. carreiro , H. charrua , H. heterogaster , H. laevior , H. megaloplax , H. montanus , H. nigricauda , H. notopagos , H. prata , H. ringueleti , and H. taimensis by having the anterior margin of the snout with an odontode-free band ( Fig. 43), vs. anterior margin of the snout completely covered by odontodes. It differ from those above by its lack of the median abdominal plate series, leaving a large naked abdominal area, plates at ventral midline restricted to small platelets at pre-anal shied region ( Fig. 8h); vs. presence of the median abdominal plate series, pre-anal shield region plated.

Description. Morphometrics and meristics in Table 12. Adult size moderate to large for members of this genus (larger than 40.0 mm in the SL). Body robust, without conspicuous keels. Caudal peduncle round in cross section, slightly flattened dorsally. Dorsal profile convex from tip of snout to dorsal-fin origin. Dorsal-fin base straight and posteroventrally sloped, straight from posterior end of dorsal-fin base to caudal-fin origin. Ventral profile somewhat concave from snout tip to posterior portion of head, almost straight from that point to anal-fin origin. Concave at anal fin base and straight 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 margin slightly concave. Head and snout broad, snout rounded to slightly pointed in dorsal view, body progressively narrowing posterior to pectoral-fin insertion. Snout region anterior to nares straight, not depressed; interorbital region straight to slightly convex. Upper margin of orbit not elevated. Eye dorsolaterally positioned. Iris operculum present.

Pectoral fin I,6. Pectoral-fin posterior margin almost straight, when depressed tip extending beyond middle of pelvic fin. Posterior margin of pectoral-fin spine smooth in adults, smaller specimens with feeble serrae along posterior third of pectoral-fin spine. Pectoral-fin axillary slit present, located below ventral margin of cleithral process. Pelvic fin i,5. Tip of depressed fin just reaching anal-fin origin in females, but extending far beyond that point in males. Dorsal II,7. Dorsal-fin origin located slightly posterior to vertical through pelvic-fin origin. Dorsal-fin spinelet 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 base of paired fins, and belly region between lateral abdominal plate series. Rostral plate with posterior notch articulation with mesethmoid. Rostral plate thickened, with odontode-free area between dorsad and ventrad series of odontodes ( Fig. 43). Snout plates anterior to nares reduced, small unplated area at lateral portion between rostral plate and prenasal plates. Three rows of predorsal plates. Lateral line incomplete, with gap without pores along middle length of body. Median plate series not truncated, reaching posterior end of caudal peduncle ( Fig. 4h). Median abdominal plate series absent. Irregularly arranged platelets in preanal shield region, absent in some specimens. Lateral abdominal plates relative small and forming regular series of three to six plates in each side ( Fig. 8g). 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 slightly larger than those of surrounding areas. Head, fin-spines, and body plates covered with odontodes, larger on anterior surface of all fin spines, and on ventral margin of rostrum, slightly enlarged on dorsal margin of rostrum. 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 round; minor (lateral) minute pointed. 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, with median notch on posterior margin of caudal-fin skeleton. Total vertebrae 29 (2 c&s).

Color in alcohol. Ground color of dorsal and lateral surfaces light brown to gray. Dorsal and lateral portions of head darker than body, except for yellowish area, contrasting with dark blotches, in ventrolateral region of head. Region anterior to nares lighter than surrounding areas, forming paired longitudinal light stripe from snout tip to posterior end of parieto-supraoccipital, bifurcating and inconspicuous from that point. Ventral surface of body pale yellow, with scattered chromatophores, mostly grouped on cheeks and base of pectoral fins forming dark blotches. Unbranched rays of pectoral, pelvic, dorsal, and anal fins mostly brown, except for narrow light bands, forming banded pattern. Branched rays of these fins mostly hyaline except for darker transverse bands. Caudal mostly dark brown, except for hyaline area on posterior portion of upper lobe. Unbranched rays of caudal fin with banded pattern of transverse light bands. In life, ground color of dorsum and flanks 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. Presence of a fleshy flap in the medial portion of first and second branched rays of pelvic fin. In juvenile males, flaps smaller or absent. Males have longer pelvic fin that extends far beyond anal-fin origin, with the pelvic fin just reaching anal-fin origin in females.

Distribution and habitat. Hisonotus heterogaster is known from the arroio Felício, a stream affluent to the rio Soturno that is a western tributary of the rio Jacuí basin ( Fig. 32). This species inhabits a median to fast flowing watercourse, with clear water running over sand or rocks, being collected mostly in the marginal submersed vegetation composed of bamboos.

Etymology. The specific epithet heterogaster , from the Greek heteros meaning distinct, deviating, abnormal, and gaster meaning belly, in allusion to the specific shape of plate covering of the abdominal plates. It is treated as a noun in apposition.