Delturus angulicauda, STEINDACHNER

Reis, Roberto E., Pereira, Edson H. L. & Armbruster, Jonathan W., 2006, Delturinae, a new loricariid catfish subfamily (Teleostei, Siluriformes), with revisions of Delturus and Hemipsilichthys, Zoological Journal of the Linnean Society 147 (2), pp. 277-299 : 288-291

DELTURUS ANGULICAUDA STEINDACHNER ( FIG. 9 )

Plecostomus angulicauda Steindachner, 1877: 672 , pl. 12 (type locality: Rio Mucuri bei Santa Clara; Rio Parahyba).

Specimens examined: Brazil: Lectotype (by present designation): NMW 44069 (188.0 mm SL), male, Rio Mucuri at Santa Clara , Bahia, 1874 . Other specimens: Minas Gerais: USNM 318209 (4 of 5, 29.6–38.5 mm SL), side branch of Rio Mucuri at Santa Clara, c. 22 km south-east of Nanuque , 23 July 1991 . USNM 315901 (3 of 4, 57.4–71.3 mm SL), side channel of Rio Mucuri at Santa Clara Farm, c. 26 km south-east of Nanuque , 5 August 1988 . MZUSP 24477 (1, 171.4 mm SL), Rio Mucuri at Nanuque , 16–18 July 1972 . MCZ 9835 (1 of 2, 210.2 mm SL), Rio Mucuri at Santa Clara, Santa Clara (17°54′S 40°13′W), December 1865 . MCZ 25769 (1, 270.3 mm SL), Rio Mucuri at Santa Clara, Santa Clara (17°54′S 40°13′W), December 1865 . USNM 318177 (1, 172.6 mm SL), Rio Mucuri, at Santa Clara, c. 22 km south-east of Nanuque , 23–24 July 1991 . USNM 318180 (3, 139.0– 165.6 mm SL), Rio Mucuri, c. 9 km from Presidente Pena on dirt road on Gavião Farm , Presidente Pena , 17–23 July 1991 . MCP 28036 (5 + 1 c&s, 94.5– 202.3 mm SL) Rio Mucuri at Nanuque , November 1997 .

Diagnosis: The posterior margin of the exposed cleithrum process tapering to a point (character 156– 1) is autapomorphic to D. angulicauda . It is also distinguished from all other Delturus by having a light brown caudal fin devoid of distinct darker spots or marks (vs. caudal fin spotted); from D. parahybae by a less deep head (head depth 46.2–54.6% SL vs. 53.9– 59.7% SL) and by tooth counts (30–52 vs. 15–24 premaxillary teeth); from D. carinotus by having a large dorsal flap on the iris (vs. dorsal flap small and inconspicuous) and a wider cleithral width (32.3–34.2% SL vs. 29.8–33.2% SL); and from D. brevis by having a concave (vs. convex) caudal fin, and a straight (vs. rounded) dorsal-fin margin.

Description: SL of examined specimens 121.3– 270.3 mm. Other morphometric data are presented in Table 2 .

Body depressed and progressively narrowing from cleithrum to end of caudal peduncle. Dorsal profile of body smoothly convex. Body arches from snout tip to end of supraoccipital process; slightly convex to straight from posterior margin of supraoccipital to origin of dorsal fin. Dorsal profile descending from origin of dorsal fin to end of caudal peduncle. Trunk mostly round in cross-section, caudal peduncle very flattened ventrally and more compressed caudally; trunk somewhat triangular at preadipose region. Greatest body depth at dorsal-fin origin. Dorsal surface of body mostly covered by dermal plates. Three to five median, preadipose plates present, forming tall ridge between dorsal and adipose fins. Lower surface of head and abdomen naked, except for some platelets sometimes embedded in skin laterally below the pectoral girdle. Median series of lateral plates with 23–26 plates; eight to 11 plates bordering dorsal-fin base; eight to ten plates between end of anal-fin base and caudal fin.

Head broad and depressed. Snout convex anteriorly. Three slightly elevated ridges between orbits and snout tip, lateral ridges more prominent. Dorsal region of head between orbits flat to slightly concave; upper margin of orbits slightly higher than interorbital space. Eyes large (orbital diameter 19.1– 21.5% HL), placed dorsolaterally. Iris with large dorsal flap. Lateral margins of head with many thin hypertrophied odontodes in mature males. Lips well developed, occupying most of ventral surface of head. Upper lip with several transversely elongate papillae. Lower lip wide, reaching anterior margin of cleithrum. Lower lip mostly covered with minute papillae, smaller posteriorly. Maxillary barbel short, free. Teeth slender, bifid, two cusps approximately equal in size ( Fig. 2 ). Premaxilla with 30–52 teeth; dentary with 31–50 teeth. Distinct skin fold present anterior to premaxillary teeth and posterior to dentary teeth.

Dorsal fin originating slightly anteriorly to or at vertical line passing through pelvic-fin origin; dorsalfin spinelet V-shaped and locking mechanism functional; one unbranched and nine to ten (usually nine) branched rays; its margin approximately straight. Fin membrane uniting last dorsal-fin ray to first preadipose plate. Pectoral fins moderate in size, with one slightly curved and flattened unbranched ray, and six branched ones. First thickened pectoralfin ray of mature males covered with large hypertrophied odontodes on anterodorsal margin. Posterior pectoral-fin margin straight to slightly round, reaching proximal third of pelvic fins when adpressed. Pelvic fins moderate in size, with one unbranched and five branched rays, not or just reaching to insertion of anal fin when adpressed. Anal fin with one unbranched and five branched rays. Caudal fin slightly concave; lowermost ray slightly longer than uppermost, 14 branched rays; three to four upper and three to four lower procurrent caudal-fin rays.

Colour in alcohol: Ground colour of dorsal surface of head and body light brown; pale yellow ventrally. Dorsum and flanks covered with dark brown, roundish blotches about size of pupil. Blotches arranged in series or forming vermiculate pattern on head and predorsal region. Blotches less conspicuous on snout. Dorsal, pectoral, and pelvic fins with indistinct dark spots along rays and interradial membranes, sometimes arranged in inconspicuous lines. Caudal fin plain light brown, without distinct darker marks. Ventral surface of head and body mostly unpigmented, except for light brown, scattered melanophores on caudal peduncle.

Distribution: Delturus angulicauda is known from several localities in the upper portions of the Rio Mucuri basin, in the State of Minas Gerais, Brazil ( Fig. 5 ).

Ecology: This species is usually found in the main river channel on a rocky bottom, where the water current is very strong.

Remarks: The type locality of D. angulicauda is problematic. Steindachner’s (1877) paper reads ‘Fundort: Rio Mucuri bei Santa Clara (nach Wertheimer) Rio Parahyba (Hartt und Copeland, Thayer Expedition)’. However, the specimen herein designated as the lectotype of Plecostomus angulicauda (NMW 44069) is certainly from the Rio Mucuri, as it shares all characters of the species common in that drainage. On the other hand, the second syntype belongs to the species inhabiting the Rio Jequitinhonha, not the Rio Paraíba do Sul, which is described below as a new species, D. brevis . The lectotype designation herein proposed for Plecostomus angulicauda is, thus, necessary for nomenclatural stability.

Figures

Figure 2. Teeth of the Delturinae. A, right premaxilary tooth of Delturus angulicauda, USNM 318180, lateral view. Scale bar 1 mm. B–H, dorsal view of right premaxillary tooth crown. B, D. parahybae, MCZ 7726. C, D. angulicauda, USNM 318180. D, D. carinotus, MCP 28039. E, D. brevis, MZUSP 69858. F, Hemipsilichthys papillatus, MCP 21423. G, H. nimius, MCP 31990. H, H. gobio, MCP 19780. Scale bar 250 µm.

Figure 5. Geographical distribution of the species of Delturus and Hemipsilichthys in south-eastern Brazil.

Figure 9. Delturus angulicauda, MCP 28036, 202.3 mm standard length, male, Rio Mucuri at Nanuque, Minas Gerais.