Delturus, 2006

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 : 295-297

DELTURUS BREVIS REIS & PEREIRA , SP. NOV.

( FIG. 12 )

Holotype: MZUSP 69858 (152.1 mm SL), male, Rio Araçuaí upstream of its mouth on Rio Jequitinhonha, Araçuaí, Minas Gerais, Brazil, 4–12 September 1989, J. C. Garavello, A. Alves, A. Soares col.

Paratypes: NMW 44070 (1, paralectotype of D. angulicauda , 171.8 mm SL), female, locality unknown . MCP 28035 (3, 138.9– 144.5 mm SL) and MZUSP 69859 (3, 136.5– 148.8 mm SL), same data as holotype . MCP 26927 (2 + 1 c&s, 86.5–146.7 mm SL), Rio Salinas , tributary of Rio Jequitinhonha, near Rubelita, Minas Gerais, Brazil (16°25′S 42°16′W), 9 November 2000, Volney Vono col.

Diagnosis: Delturus brevis is distinguished from all other Delturus by its convex caudal fin (vs. concave) and rounded dorsal-fin margin (vs. straight); from D. angulicauda by having spots on the caudal fin (vs. caudal fin unspotted); from D. carinotus by its wider body (cleithral width 33.2–35.2% SL vs. 29.8–33.2% SL) and by having a large dorsal flap on the iris (vs. flap very small); from D. parahybae by having eight to nine plates between the end of the anal-fin base and the caudal fin (vs. ten to 11), 22–24 lateral plates in the median series (vs. 26–28), by more numerous premaxillary teeth (26–137 vs. 15–24), and by its less deep head (head depth 50.7–54.1% HL vs. 53.9–59.7% HL).

Description: SL of examined specimens 136.0– 152.1 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 tip of supraoccipital to origin of dorsal fin. Dorsal profile then descends from origin of dorsal fin to end of caudal peduncle. Trunk mostly round in cross-section, caudal peduncle 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. Four to six 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 22–24 plates; six to eight plates bordering dorsal-fin base; eight to nine plates between end of anal-fin base and caudal fin.

Head broad and depressed. Snout convex anteriorly. Three indistinctly elevated ridges between orbits and snout tip. Dorsal region of head between orbits concave; upper margin of orbits distinctly higher than interorbital space. Eye large (orbit diameter 20.3– 24.5% HL), placed dorsolaterally. Iris with large dorsal flap. Lateral margins of head with patch of 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 very 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 26–137 teeth; dentary with 22–133 teeth. Distinct skin fold present anterior to premaxillary teeth and posterior to dentary teeth.

Dorsal fin originating slightly anterior to vertical line passing through pelvic-fin origin; dorsal-fin spinelet V-shaped and locking mechanism functional; one unbranched and eight to nine (usually nine) branched rays; its margin strongly rounded. Fin membrane uniting last dorsal-fin ray to first preadipose plate or terminating just anterior to first preadipose plate. Pectoral fins moderate in size, with one slightly curved and flattened unbranched ray, and six branched ones. First thickened pectoral-fin ray of mature males covered with large hypertrophied odontodes on anterodorsal margin. Posterior pectoral-fin margin slightly round, reaching proximal third to half-length of pelvic fins when adpressed. Pelvic fins moderate in size, with one unbranched and five branched rays, not or just reaching origin of anal fin when adpressed. Anal fin with one unbranched and five branched rays. Caudal fin distinctly convex; 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. Plates of dorsum and flanks darker anteriorly and lighter posteriorly, forming a barred or reticulate pattern. Markings usually more conspicuous and thicker on head forming a vermiculate pattern. All fins with dark bands, sometimes discontinuous and forming indistinct large spots. Ventral surface of head and body mostly unpigmented, except for light brown, scattered melanophores on caudal peduncle and upper lip.

Distribution: Delturus brevis is known from two localities in the upper portions of the Rio Jequitinhonha basin, in the state of Minas Gerais, Brazil ( Fig. 5 ).

Ecology: All specimens were collected in a strong water current on a rocky bottom.

Etymology: From the Latin brevis , an adjective meaning short. In allusion to the smaller maximum size of this species compared with the others and to the comparatively reduced counts of some plates and dorsalfin rays.

Remarks: Despite being labelled as from the Rio Mucuri, the paralectotype of D. angulicauda (NMW 44070) is in fact a specimen of D. brevis , and is herein included as a paratype of this new species. As D. brevis has only been collected in the Rio Jequitinhonha drainage, and because this river is very close to the Rio Mucuri, we believe that the specimen in NMW 44070 has actually been collected in the Rio Jequitinhonha and mislabelled as from Rio Mucuri. The type locality of Plecostomus angulicauda , however, includes Rio Mucuri and Rio Paraíba do Sul, and this is also a mistake (see Remarks under D. angulicauda ).

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 12. Delturus brevis, holotype, MZUSP 69858, 152.1 mm standard length, Rio Araçuaí upstream of its mouth on Rio Jequitinhonha, Araçuaí, Minas Gerais.