Steindachneridion parahybae ( Steindachner, 1877 )

Garavello, Julio Cesar, 2005, Revision of genus Steindachneridion (Siluriformes: Pimelodidae), Neotropical Ichthyology 3 (4), pp. 607-623 : 610-612

Steindachneridion parahybae ( Steindachner, 1877) Fig. 2

Platystoma Parahybae Steindachner, 1877: 640 , pl.9, syntypes MCZ 73213, MCZ 25521, and MCZ 7295 (examined).Type locality: rio Parahyba at Juiz de Fora ; rio Jequitinhonha, Brazil.

Steindachneria parahybae: Eigenmann & Eigenmann, 1888: 137 (types); Eigenmann & Eigenmann, 1890: 204; fig. 48 (types, description) Eigenmann, 1910: 391 (ref.); Ribeiro, 1902: 255 (rio Pomba); Ribeiro, 1911: 299 (458), pl, 43 (rio Pomba).

Steindachneridion parahybae: Gosline, 1945: 51 (ref.); Fowler, 1951: 603 (rio Paraíba, rio Jequitinhonha, Uruguay); Burgess, 1989: 282; Lundberg et al., 1991: 842; Oliveira & Moraes Junior, 1997: 3; Lundberg & Littmann in Reis et al., 2003: 443.

Diagnosis. Steindachneridion parahybae differs from the remaining species of the genus by the following combination of characters: supraoccipital process almost in contact with anterior nuchal plate; premaxillary tooth plates large, separated by a medial groove and curved distally; vomer in adults and juveniles with in a single plate; 16-18 gill rakers on first branchial arch; caudal fin slightly notched; orbit moderately large, 9.3 to 11.7% of HL and 26.5 to 38% of interorbital distance; maxillary barbel short, reaching or surpassing the origin of the pectoralfin insertion; pectoral and adipose fins short; pelvic fin very short, never reaching the anus. Ground color in alcohol light grayish, abdomen whitish, large dark brown blotches irregularly distributed over head and trunk in an irregular, vermiculated or dotted pattern; caudal peduncle low, its depth 30.8 to 33.9% of HL; head depth comprising 70.8 to 86.2 of % of head width; and head width moderately large, 22 to 24.7% of SL.

Description. Morphometric data presented in Table 1; maximum body length 384 mm SL. Snout long; snout tip roughly rounded in dorsal view; 12.1 to 13.4% of SL; each pair of nostrils protruding on dorsal snout profile; anterior pair of nostrils more widely spaced apart than posterior pair. Head short and high in dorsal view, and slightly depressed in lateral view; head depth 70.8 to 86.2% of head width; head depth 15.8 to 18.9% of SL; head length 27.5 to 29.4% of SL. Dorsal profile of head almost straight from tip of snout to anterior nuchal plate; slightly elevated at orbital region; supraoccipital process almost in contact with anterior nuchal plate. Eye dorsally placed midway between snout tip and opercular opening; orbit moderately large, orbital diameter 9.3 to 11.7% of HL and 26.5 to 38% of interorbital distance.

Opercular opening large and branchial membranes joining at narrow isthmus; eight branchiostegal rays; 16-18 gill-rakers on first branchial arch. Lower region of head with arrow-like, shallow gular fold; deep grooves at lower jaw posterior margin. Mouth large and terminal; mouth width 48 to 51.1% of HL; lower jaw shorter than upper jaw; lips thin; posterior postcleithral process short, reaching vertical line passing near posterior margin of supraoccipital process; all barbels narrow and compressed; maxillary barbel very short, reaching or only slightly surpassing anterior insertion of dorsal fin when adpressed; pair of short mental and post-mental barbels on each side. Tooth plates of premaxilla and dentary with villiform teeth; premaxillary tooth plates large; abruptly narrowing and curved inward distally; single vomerine tooth plate grooved medially in adults and juveniles, circumscribed by premaxillary tooth plate; dentary plate large and distally sharp.

Body profile slight convex between posterior head and dorsal-fin origin; dorsal-fin base slanted; base of adipose fin almost straight; dorsal profile of caudal peduncle deeply concave from end of adipose fin to caudal-fin origin. Predorsal length moderately long, 36.4 to 39.7% of SL. Ventral profile of body almost straight and slightly slanted from tip of snout to end of opercular bone; slightly convex at middle abdominal region, straight at pelvic-fin insertion; base of anal fin slanted; lower caudal peduncle profile slightly concave; cross section of caudal peduncle at vertical through posterior tip of anal fin approximately oval. Dorsal-fin rays i,7 (6 or 8) first two more or less spinous; dorsal-fin base inserted in dorsal space between vertical through pectoral-fin terminus and analfin origin; dorsal-fin locking mechanism present. Pectoral fin short, fin tip not reaching vertical through middle dorsal-fin insertion; rays i,9 (10), posterior margin truncate; first pectoral-fin ray short and not pungent, both margins devoid of serrae. Pelvic fin short; i,5 rays, fin never reaching anus; tip of unbranched pelvic-fin ray smooth; distal margin of fin truncate; pelvic fin distant from anal-fin origin and inserted at vertical through dorsal-fin insertion, its tip not reaching anus or vertical passing through adipose-fin origin. Anal-fin rays short, i,8 (9,10), distal margin truncate; preanal distance 68 to 72.5% of SL. Caudal peduncle high, its depth 8.7 to 9.3% of SL. Caudal fin notched, dorsal lobe slightly longer than ventral lobe; principal caudal-fin rays, i,15,i.

Body and head, except orbital region covered with thick skin. Ventral surfaces of pectoral and pelvic girdle entirely covered by skin; supraoccipital process short and covered by thin skin anterior to first unbranched dorsal-fin ray, as in S. doceanum and S. amblyurum . Postcleithral process short and entirely covered by skin.

Color in alcohol. Ground color of head, dorsum, and lateral regions of body light gray, ventral region whitish; dorsal and lateral portions of head and trunk with large irregularly distributed dark brown lines, forming bold vermiculated color pattern of dark brown and light gray lines. Eye dark. Dorsal, pectoral, pelvic, anal, and adipose fins uniformly light gray with dark brown lines on rays and membranes; adipose fin with several dark brown lines; caudal fin with dark lines on base of each lobe, gray distally.

Distribution. Known from the rio Paraíba do Sul basin, eastern Brazil ( Fig. 1 ).

Material examined Rio de Janeiro State: MCZ 7295 (syntype), 1, 278.0 mm SL, rio Paraíba do Sul, between Barra do Piraí and Três

Rios (D. Pedro II railroad), Apr 1865 (approx. 22°6’S 43°11’W). Três Rios: MNRJ 12235 , 1, 265 mm SL, rio Paraibuna, at connection with rio Paraíba do Sul , Jun 1989 (approx. 22°6’S 43°11’W) . MNRJ 12237 , 1, 384 mm SL and MNRJ 12302 , 1, 295mm SL, rio Paraíba do Sul, at confluence with rio Piabanha and rio Paraibuna , Pontal , Dec 1989 (approx. 22°7’S 43°9’W) . MNRJ 12238 , 1, 337 mm SL; MNRJ 12239 , 1, 324 mm SL; MNRJ 12240 , 1, 250 mm SL and MNRJ 12303 , 1, 300 mm SL, rio Paraíba do Sul, at confluence with rio Piabanha and rio Paraibuna , Pontal , Jan 1990 (approx. 22°7’S 43°9"W). MNRJ 12301 , 1, 327 mm SL, rio Paraíba do Sul , at confluence of Paraibuna and Piabanha rivers, Pontal , Oct 1989 (approx. 22°7’S 43°9"W) . MNRJ 12303 , 1, 300 mm SL, rio Paraibuna, at confluence with rio Piabanha and rio Paraibuna , Pontal , Feb 1990 (22°7’S 43°9’W) .

Figures

Fig 2. Lateral and dorsal views of S. parahybae. MNRJ 12237, 384 mm SL, rio Paraíba do Sul, at confluence with rio Piabanha and rio Paraibuna, Pontal, Rio de Janeiro, Brazil.

Fig. 1. Southeastern South America with the geographical distribution of Steindachneridion species. Each symbol may represent more than one sample.