Scoloplax baskini, Rocha & Oliveira & Rapp Py-Daniel, 2008

Rocha, Marcelo Salles, Oliveira, Renildo Ribeiro de & Rapp Py-Daniel, Lúcia H., 2008, Scoloplax baskini: a new spiny dwarf catfish from rio Aripuanã, Amazonas, Brazil (Loricarioidei: Scoloplacidae), Neotropical Ichthyology 6 (3), pp. 323-328 : 324-325

Scoloplax baskini , new species

Figs. 1- 3 , 4e , 5

Holotype. INPA 28658 , 14.4 mm SL, Brazil, Amazonas, Novo Aripuanã, rio Aripuanã, igarapé Palhalzinho , 5º59'32.3''S 60º12'35''W, 6 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira . Paratypes. Brazil, Amazonas, Novo Aripuanã, rio Aripuanã drainage : ANSP 187488 , 3 , 12.5-13.1 mm SL, igarapé Palhalzinho, 5º59'32.3''S 60º12'35''W, 6 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira; INPA 28649 , 42 , (20, 11.1-17.2 mm SL; 6 cs, 11.2-12.8 mm SL), igarapé Palhalzinho, 5º59'32.3''S 60º12'35''W, 6 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira; INPA 28650 , 24 , (10, 10.7-16.1 mm SL; 4 cs, 11.8-16.1 mm SL), lago do Mamão, shore, 6º08'48''S 60º11'47.9''W, 8 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira; INPA 28651 , 1 , 11.2 mm SL, igarapé da Cachoeira, just above first waterfall, close to mouth of igarapé, 6º24'39.53''S 60º21'41.06''W, 11 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira; INPA 28652 , 29 (4 cs, not measured), igarapé Palhalzinho, 5º59'32.3''S 60º12'35''W, 10 Sep 2004, L. H. Rapp Py-Daniel, L.M. de Sousa & O.M. Ribeiro ; MCP 43133, 3 , 10.5-13.7 mm SL, igarapé Palhalzinho, 5º59'32.3''S 60º12'35''W, 6 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira; MPEG 14754 , 3 , 12-12.3 mm SL, igarapé Palhalzinho, 5º59'32.3''S 60º12'35''W, 6 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira; MZUSP 99301 , 3 , 12.7-14.8 mm SL, igarapé Palhalzinho, 5º59'32.3''S 60º12'35''W, 6 Sep 2007, L. H. Rapp Py-Daniel, M. S. Rocha & R. R. de Oliveira.

Diagnosis. The new species can be distinguished from other Scoloplax by the following unique features: ventral midline plates between the anus and caudal peduncle with two longitudinal parallel rows of odontodes not covered by skin; pectoral and pelvic fins with all rays simple, unbranched; larger specimens with odontodes in abdominal area between pelvic-fin bases and immediately anterior to genital papilla; mesethmoid with thickened triangular anterior process; and larger specimens with small odontodes on first and second pelvic-fin rays.

Description. Morphometrics given in Table 1. Small size, 10.5- 17.2 mm SL. Head and body strongly depressed. Dorsal profile of head and predorsal area nearly straight except for shallow depression at posterior tip of rostral plate. Body profile straight between dorsal and caudal fins. Snout rounded in dorsal view. Head with series of odontodes forming lateral ridge from orbit to posterior pterotic-supracleithrum spine. Small bony plate located immediately lateral to lateral ethmoid and just anterior to orbit [“lateral ethmoid plate” sensu Schaefer (1990)] bearing three to five odontodes near posterior margin ( Fig. 3 ). Rostral plate bearing 14-24 recurved odontodes. Eye dorsal and conspicuous.

Mouth small, terminal. Maxillary barbel biramous, major ramus elongate, reaching base of pectoral-fin spine; minor ramus short, not reaching base of pectoral-fin spine. Mental barbel uniramous, origin anterior to gular fold and posterior to mandibular symphysis. Mandibular barbel uniramous, origin at corner of mouth.

Small platelet at distal tip of rib on sixth vertebra bearing 3-16 small odontodes. Odontodes present on posterior coracoid process. Mesethmoid with a thickened triangular anterior process ( Figs. 3 , 4e ). Four branchiostegal rays.

Dorsal fin with spinelet, spine and three soft branched rays. Dorsal spine with small odontodes. Locking mechanism present. Pectoral fin with well-developed spine and four unbranched rays. Pectoral spine completely covered with small odontodes and with few small serrations along posterior margin from mid-length to distal tip; locking mechanism present. Pelvic fin with four unbranched rays; first ray thicker and with odontodes. In larger specimens the second pelvic-fin ray bears a few small odontodes.Anal fin with five to six rays. First ray unbranched, thickened and bearing odontodes, followed by three to four branched rays and with the last ray unbranched. Caudal fin with 11 rays; outer rays unbranched and bearing small odontodes. Nine principal inner rays branched near tips. Procurrent caudal-fin rays absent.

Dorsolateral plates 16-17, extending posteriorly from base of last dorsal-fin ray to caudal peduncle. Ventrolateral plates 8-9. Ventral midline plates 4-6, bearing odontodes along lateral margins forming two longitudinal rows ( Fig. 5 ). Total vertebrae 25-27 (n=10).

Coloration. Body overall brownish, more pigmented laterally with wide longitudinal dark brown stripe along lower region of trunk from pectoral to caudal fin ( Figs. 1-2 ). Mid-ventral plate series less pigmented. Dorsal part of body pale except for three narrow dark saddles. First saddle faint, at dorsal fin origin; other two saddles darker and evenly spaced between dorsal and caudal fins. Ventral portion of body pale, creamcolored, sometimes with dark pigment concentrated along lateral edges and more diffuse pigment across abdomen. Dorsal fin darkly pigmented along base and hyaline distally. Pectoral fin largely hyaline except for dark spots clustered in spear-like submarginal band. Pelvic fin largely hyaline except for faint dark submarginal band. Anal fin with two thin dark transverse bands, one near base and the other near mid-length. Base of caudal fin with dark brown spot extending anteriorly onto caudal peduncle. Remaining caudal fin hyaline except for dark pigment forming blotchy subterminal distal band.

Distribution. Scoloplax baskini was found among leaf litter in small clearwater tributaries of the middle part of rioAripuanã, a right-bank tributary of the middle rio Madeira ( Fig. 6 ).

Etymology. Species name in honor of Jonathan Baskin for his significant contributions to Neotropical ichthyology including the description of the genus Scoloplax .

Figures

Fig. 1. Scoloplax baskini, INPA 28658, holotype, 14.4 mm SL. Photo by R. R. de Oliveira.

Fig. 2. Scoloplax baskini, INPA 28649, paratype, 16.3 mm SL, in lateral (top), dorsal (middle) and ventral (bottom) views. Illustration by Deyse Silva.

Fig. 3. Partial cranial osteology of Scoloplax baskini, INPA 28650, paratype, 16.1 mm SL, anterior towardleft.Rostral plate removed. f = frontal; me = mesethmoid; le = lateral ethmoid; lep = lateral ethmoid plate; so = supraoccipital; sp = sphenotic. Scale = 0.5 mm.

Fig. 4. Partial cranial osteology in Scoloplax. a, S. dicra; b, S. distolothrix; c, S. empousa; d, S. dolicholophia; e, S. baskini, INPA 28650, paratype, 11.8 mm SL.Anterior toward left. Rostral plate and lateral ethmoid plate removed. f = frontal; me = mesethmoid; le = lateral ethmoid. Scale = 0.5 mm. Figures a-d modified from Schaefer (1990).

Fig. 5. Ventral midline plates in Scoloplax baskini, INPA 28650, paratype, 16.1 mm SL. Ventral view, anterior toward left.

Fig. 6. Partial map of South America showing the type localities of species of Scoloplax. Square = Scoloplax baskini new species; black circle = S. dolicholophia; open circle = new record of S. dolicholophia from Japurá basin; triangle = S. distolothrix; diamond = S. empousa; star = S. dicra. Base map by M. Weitzman.