Steindachneridion amblyurum (Eigenmann & Eigenmann, 1888)

Garavello, Julio Cesar, 2005, Revision of genus Steindachneridion (Siluriformes: Pimelodidae), Neotropical Ichthyology 3 (4), pp. 607-623 : 612-613

Steindachneridion amblyurum

( Eigenmann & Eigenmann, 1888)

Figs. 3-4

Steindachneria amblyurus Eigenmann & Eigenmann, 1888: 137 , syntype MCZ 7324 (examined) Type locality: rio Jequitinhonha , Brazil.

Steindachneria amblyurus: Eigenmann & Eigenmann, 1888: 137 (types).

Steindachneria amblyura: Eigenmann & Eigenmann, 1890: 203 ; fig.27. Eigenmann & Eigenmann 1891: 31 (ref.); Eigenmann, 1910: 391 (ref.); Ribeiro, 1911: 300 (458).

Steindachneridion amblyura: Gosline, 1945: 51 (ref.); Fowler, 1951: 603 (ref.); Burgess, 1989: 282 (ref.).

Steindachneridion amblyurus: Lundberg & Littmann in Reis et al., 2003: 443.

Platystoma parahybae Steindachner (part) 1876: 640 (rio Jequitinhonha).

Diagnosis. Steindachneridion amblyurum differ from its congeners by the following combination of characters: supraoccipital process almost in contact with anterior nuchal plate. Premaxillary tooth plates large, grooved in median region and sharply curved in distally; tooth plate on vomer in adults and juveniles divided in two almost oval sections laterally disposed; 13-14 gill-rakers on first branchial arch. Caudal fin distally rounded; orbit small, 9.8 to 10.8% of HL and only 24.2 to 28% of interorbital distance; maxillary barbel long, reaching or surpassing the base of the adipose-fin insertion; pectoral, adipose and pelvic fins large sized; pelvic pair very long, concealing the anus; distal margin of dorsal fin almost reaching the adipose-fin insertion; adipose fin larger than anal-fin. Color in alcohol with dark brown large lines irregularly distributed on head and trunk, with large dorsal black dots between lines, over a yellowish ground color; caudal peduncle low, its depth 32.4 to 37.4% of HL; head depth low, 65.1 to 79.6% of head width; head width small, 35.6 to 38% of SL.

Description. Morphometric data presented in Table 1; maximum body length, 334 mm SL. Snout slender and very depressed; snout tip elliptical in dorsal view; snout length 12 to 13.6% of SL; two pair of nostrils horizontally aligned, anterior pair of nostrils in the same distance as nostrils of posterior pair; each pair of nostrils protruding on dorsal snout profile. Head long in dorsal view, very low and depressed in lateral view; head depth 65.1 to 79.6% of head width; head depth 13.8 to 18.5% of SL; head length 27 to 29.5% of SL. Dorsal profile of head almost straight from tip of snout to nuchal plate; slightly high at orbital and supraoccipital regions. Eyes dorsally placed and inserted near snout tip than opercular opening; orbit small, its diameter 9.8 to 10.8% of HL and 24.2 to 28% of interorbital distance. Supraoccipital short covered by thin skin, almost reaching nuchal plate.

Opercular opening large; branchial membranes joining to narrow isthmus; eight branchiostegal rays; 13-14 gill-rakers on first branchial arch. Lower region of head with arrow-like shallow gular fold; deep grooves at posterior margins of lower jaw. Mouth large and terminal; mouth width 52.1 to 57.1% of HL; lower jaw shorter than upper and with thin lips; posterior postcleithral process short, reaching vertical line through posterior supraoccipital process. All maxillary barbels, narrow and depressed; maxillary barbel very long, reaching or only slightly surpassing insertion of adipose fin when adpressed; pair of short mental and post-mental barbels on each side. Tooth plates of premaxillary and dentary with villiform teeth; premaxillary tooth plate slender, medially grooved; sharply curved distally; vomerine tooth plate in adults and juveniles, divided in two small elliptical plates at median region; both circumscribed by premaxillary tooth plate; a single and elongated dentary tooth plate, distally sharp.

Body profile slight convex between head and adipose-fin origin; dorsal-fin base slanted; base of adipose fin almost straight; dorsal profile of caudal peduncle deep concave from end of adipose fin base to caudal-fin origin. Predorsal length short, 35.6 to 38% of SL. Ventral profile of body almost straight and slightly inclined from tip of snout to end of opercular bone, slightly convex or almost straight at middle inferior head and abdominal region, almost flat on 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); dorsal-fin base inserted in the dorsal space between the vertical through the pectoral-fin terminus and the anal-fin origin; dorsal-fin locking mechanism present. Pectoral-fin long and not pungent, reaching the vertical line through middle dorsal-fin base; rays i,9(10); first pectoral-fin ray short and not pungent, both margins devoid of serrae. Pelvic fin long, i,5; inserted at vertical at end of dorsal-fin, concealing the anus and reaching the anal-fin insertion; tip of unbranched pelvic-fin ray smooth; distal margin slightly rounded. Analfin rays elongated i,8(9), distal margin rounded; preanal distance 68.1 to 71.6% of SL; first anal-fin ray smooth, not pungent; its distal margin rounded. Adipose fin very large, leaving a narrow space between dorsal and adipose fin; base of adipose fin almost straight. Caudal peduncle low, its depth 9.2 to 10.2% of SL. Caudal fin distally rounded, upper and lower lobes equal; principal caudal-fin rays, i,15,i.

Body and head, except orbital region, covered with thick layer of skin; scapular bridge and pelvic girdle also entirely covered by skin. Supraoccipital process and anterior nuchal plate covered by thin skin and almost in contact. Posterior postcleithral process short and entirely covered by thick skin.

Color in alcohol. Ground color of dorsal and lateral regions of body light brown; ventral region yellowish; dorsal and lateral portions of head, snout, and trunk with irregularly distributed dark brown large lines, sometimes with large black dots on dorsum; lower region of head and abdomen yellow. Eyes dark. Dorsal, pectoral, pelvic, anal and adipose fins uniformly light gray with black lines or black dots on rays and membranes; several dark brown lines and dots on adipose fin; caudal fin with dark lines and small dots on base, but distally gray.

Distribution. Known from the rio Jequitinhonha basin, Brazil ( Fig. 1 ).

Material examined. Minas Gerais State: MCZ 7324 (syntype), 1, 380 mm SL, rio Jequitinhonha, along Jequitinhonha valley , 4 May 1866 . MZUSP 87986 , 1, 334 mm SL, Almenara, rio Jequitinhonha, ilha Bela Vista , 27 Feb 1989 . MZUSP 87987 , 1, 261 mm SL, rio Araçuaí, near confluence with rio Jequitinhonha, Itira , Feb 1989 . LISDEBE 1160, 3, 261- 301 mm SL, Araçuaí, rio Jequitinhonha, downriver from the rio Araçuaí confluence, 17-20 Jan 1989 .

Figures

Fig. 3. Lateral and dorsal views of S. amblyurum. MZUSP 87986, 334 mm SL, Almenara, rio Jequitinhonha, ilha Bela Vista, Minas Gerais, Brazil.

Fig. 4. Lateral view of S. amblyurum syntype. MCZ 7324, 380 mm SL, rio Jequitinhonha, along Jequitinhonha valley, Minas Gerais,Brazil.

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