Steindachneridion Eigenmann & Eigenmann, 1919

Garavello, Julio Cesar, 2005, Revision of genus Steindachneridion (Siluriformes: Pimelodidae), Neotropical Ichthyology 3 (4), pp. 607-623 : 608-610

Genus Steindachneridion Eigenmann & Eigenmann, 1919

Steindachneria Eigenmann & Eigenmann, 1888: 137 , type species Steindachneria amblyurus Eigenmann & Eigenmann, 1888 . Name preoccupied by Steindachneria Goode & Bean, 1888 in fishes, replaced by Steindachneridion Eigenmann & Eigenmann, 1919 ; Eigenmann & Eigenmann, 1890: 202 (diagnosis and key); Ribeiro, 1902: 255; Ribeiro, 1911: 299 (458).

Steindachneridion Eigenmann & Eigenmann, 1919:525 , Type species Steindachneria amblyurus Eigenmann & Eigenmann, 1888 . Replacement for Steindachneria Eigenmann & Eigenmann, 1888 ; Gosline, 1945: 51 (ref.); Fowler, 1951: 602 (ref); López, Menni & Miquelarena, 1987:27 (ref.); Burgess, 1989: 282 (ref); Lundberg et al., 1991: 842; Oliveira & Moraes Junior, 1997: 3 (ref); de Pinna, 1998: 314; Lundberg & Littmann in Reis et al., 2003: 443.

Diagnosis. Large sized pimelodid fishes, up to 1000 mm or more; head short and depressed without external exposed ossification and covered by skin; supraoccipital process not reaching the anterior nuchal plate; postcleithral and pelvic girdle short and entirely covered by thick skin. Eye small, dorsally located in the anterior surface of head and with orbital margin free. Teeth on premaxilla and dentary in villiform tooth patches grooved at medial region; vomerine teeth arranged in one or two tooth plates, the anterior arched; 12 to 17 gill-rakers on first branchial arch; dorsal-fin i,6 (7-8) rays; pectoral fin i,9 (10) rays; pelvic fin i,5 rays; anal fin i,8 (9,10) rays. Principal caudal-fin rays, i,15(14-16),i; maxillary barbel long, extending from tip of snout to base of dorsal or base of adipose fin; adipose fin base longer than anal-fin base. Caudal fin notched with the exception of S. amblyurum , were it is distally rounded. Ground color dark brown in S. melanodermatum and light brown or grayish on the remaining species; marbled, lined or dotted with dark brown lines or dots place over the head, dorsum, lateral trunk and fins.

Comparisons. Steindachneridion is distinguished from other genera of the Pimelodidae by a combination of features whose phylogenetic relationships are not yet fully determined. Combined characteristics shown to be useful for comparisons and for the identification of an affinity species group whose features, some of them derived, support the genus. The combination of: (1) supraoccipital process short (reduced) and externally not meeting the anterior nuchal plate; (2) tooth plates of premaxilla and dentary with villiform teeth, premaxilla and dentary with patch grooved at medial region and vomer with one or two isolated tooth plates; (3) head relatively small, covered by thick skin; (4) eyes relatively small, with orbital margin free; (5) eight branchiostegal rays; (6) seven dorsalfin rays; (7) low dorsal fin with short dorsal fin spine, not pungent; (8) pectoral fin spine short, not pungent and with both margins devoid of serrae; (9) 12 to 17 gill-rakers on first branchial arch; (10) relative long and straight-margined adipose fin; and caudal fin notched, except in S. amblyurum , furnish the differential diagnosis for the genus.

By these characters and other expressed in the species descriptions, Steindachneridion shares a basal position with other genera of group A of the Pimelodidae as proposed by Lundberg et al. (1991). According to the hypothesis raised by the aforementioned authors, the relationships of Steindachneridion lies in a polytomy with other pimelodid genera, among them, Sorubimichthys , Pseudoplatystoma , Hemisorubim , Brachyplatystoma , Sorubim and Platynematichthys . On the other hand, Figueiredo & Costa-Carvalho (1999) discuss some cranial characters of the fossil species S. silvassantosi and suggest that it shares features with, and may be related to, the genera Leiarius , Phractocephalus , and Lophiosilurus . A more basal position for the genus Steindachneridion is suggested by Lundberg & Akama (2005) and some information about a forthcoming contribution presenting some molecular evidence that this genus may be included in the Phractocephalus group is available. Unfortunately the phylogenetic relationships of genus Steindachneridion within the family Pimelodidae are not resolved, remaining only partially known. The characters studied herein may furnish new data for comparisons and discussions, and justify the taxonomic revision of genus Steindachneridion Eigenmann & Eigenmann, 1919 . In fact, this genus is actually included in the catfish family Pimelodidae as delimited by Lundberg & Littman (2003), a monophyletic assemblage of small to large sized fishes, currently including 29 genera and 84 species.

Nomenclatural note. Steindachneridion is neuter ( Lundberg & Littmann, 2003), therefore, the specific names amblyurus , doceana , scripta , and punctata are emended below to amblyurum , doceanum , scriptum , and punctatum .

Distribution. Known from Southeastern Brazilian drainages of Jequitinhonha, Doce, Paraíba do Sul, upper Paraná and Uruguay rivers, Brazil ( Fig. 1 ).

Key to the species of Steindachneridion .

1. Supraoccipital process elongated, extending to near or almost meeting anterior nuchal plate in dorsal view ......... 2

1´. Supraoccipital process short, distance from anterior nuchal plate one or two times orbital diameter in dorsal view ..... 4

2. Tooth plate on vomer in adults divided in two sections and laterally placed on palate; caudal fin distally rounded; 12- 14 gill-rakers on first branchial arch; small orbit, 9.8 to 10.8% of HL and 24.2 to 28% of interorbital distance; maxillary barbel long, reaching or surpassing base of adiposefin insertion ....................................... S. amblyurum [p. 612]

2’. Tooth plate on vomer in adults in contact or continuous in single section on palate; caudal fin notched; 12-18 gillrakers on first branchial arch; large orbit, 10.3 to 11.7% of HL and 30.4 to 35% of interorbital distance; maxillary barbel short, when adpressed, reaching or surpassing only middle of pectoral fin ........................................................... 3

3. Pectoral, adipose and pelvic fins large sized; pelvic pair long, always surpassing and almost concealing anus; color pattern marbled, alternating dark brown, large bowed lines with ground yellowish lines; 18-20 gill rakers on first branchial arch .................................... S. doceanum [p. 613]

3´. Pectoral, adipose and pelvic fins small sized; pelvic fin short, never reaching anus; color pattern combining dark brown lines with large dark brown dots on dorsum of head and trunk; 15-17 gill-rakers on first branchial arch ........... ............................................................. S. parahybae [p. 610]

4. Supraoccipital process separated from the anterior nuchal plate by a space covered with thick skin, corresponding to two orbital diameters; large concentration of dark melanophores producing dark brown ground color, combined with minute black dots on dorsum of head and trunk; 16- 18 gill-rakers on first branchial arch .................................. ................................................. S. melanodermatum [p. 618]

4´. Supraoccipital process separated from the anterior nuchal plate by a space covered with thick skin, corresponding to one orbital diameter; ground color light gray, with large black lines or black dots irregularly distributed on dorsum of head and trunk ................................................................. 5

5. 15-17 gill-rakers on first branchial arch; large black lines irregularly distributed; orbit small, 21.2 to 31.7% of interorbital distance and 7.3 to 10.1% of HL ..... S. scriptum [p. 615]

5´.12-14 gill-rakers on first branchial arch; large black dots irregularly distributed; orbit large, 26.4 to 36.5% of interorbital distance and 8.6 to 11.7% of HL ............................. ............................................................ S. punctatum [p. 616]

Figures

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