Isbrueckerichthys calvus, Fernando C. Jerep, Oscar A. Shibatta, Edson H. L. Pereira & Osvaldo T. Oyakawa, 2006

Fernando C. Jerep, Oscar A. Shibatta, Edson H. L. Pereira & Osvaldo T. Oyakawa, 2006, Two new species of Isbrueckerichthys Derijst, 1996 (Siluriformes: Loricariidae) from the rio Paranapanema basin, Brazil., Zootaxa 1372, pp. 53-68 : 60-65

Isbrueckerichthys calvus , new species

Fig. 2.

Holotype. MZUEL 3714; 87.3 mm SL; male; Brazil; Paraná State; Apucarana; rio Tibagi basin; córrego Juruba; 23º34’44.6”S / 51º22’12.6”W; 08 September 2005; F. C. Jerep, E. S. da Silva, A. Souza.

Paratypes. MZUEL 3724; 9 (6) 65.5-90.2 mm SL; MCP 40208; 2 (2) 72.55-86.24 mm SL; collected with the holotype. MCP 40207; 2 (2) 46.36-67.08 mm SL; Califórnia; rio Tibagi basin; ribeirão Água dos Oito; 21 October 2004; F.C. Jerep, E.S. da Silva, A. Souza. MZUSP 90804; 3 (3) 63.0-73.5 mm SL; Apucarana; rio Tibagi basin; córrego Juruba; 23º33’58.2”S / 51º24’17.4”W; 08 September 2005; F.C. Jerep, E.S. da Silva, A. Souza. MZUEL 3638; 5 (4) 42.4-78.8 mm SL; Califórnia; rio Tibagi basin; ribeirão Água dos Oito; 21 October 2004; F. C. Jerep, E. S. da Silva, A. Souza. MZUEL 3715; 1 (1) 65.6 mm SL; Califórnia; rio Tibagi basin; ribeirão Água dos Oito; 19 Oct 2000; A. Souza.

Diagnosis. Isbrueckerichthys calvus can be distinguished from I. alipionis by having bifid teeth, with a small lateral cusp (vs. teeth without lateral cusp). Differ from I. epakmos , by mature males having margins of the head with thin fleshy lobes (vs. soft and rugose fleshy area well developed on anterior portion of snout of mature males) and by the presence of short hypertrophied odontodes along the lateral margin of head (vs. presence of a clump of hypertrophied odontodes located only on anterior portion of snout, directed forward or slightly upwards). Differ from I. duseni by having a longer pectoral-fin spine (21.5-26.4 % vs. 17.3-21.4 % SL) and a shorter caudal peduncle length (26.4-29.7 % vs. 34.6-38.2 % SL). Differ from I. saxicola by having minute abdominal platelets with at most six odontodes (vs. minute abdominal platelets with much more than six odontodes, frequently 12); nude area under the first three plates of the lateral line (Fig. 3) (vs. plated area under the first three plates of the lateral line); cleithrum not exposed, or when exposed, bordering just the superior portion of posterior margin of the opercular opening on lateral side of the body (Fig. 3) (exposed portion of cleithrum bordering all the posterior margin of the opercular opening); exposed surface of supraoccipital strongly convex, with an area without odontodes on the center (vs. exposed surface of supraoccipital plane or slightly convex).

Description. Counts and proportional measurements presented in Table 1. Dorsal surface of the body covered by plates except for naked area around dorsal fin. Body moderately depressed. Progressively narrowing from cleithrum to end of caudal peduncle. Dorsal profile of the body slightly convex, rising from snout tip to origin of dorsal fin and then descending to end of caudal peduncle. Trunk and caudal peduncle mostly ovoid in cross-section, slightly flattened ventrally and more compressed caudally. Greatest body depth at dorsal-fin origin. Ventral surface of the head, region from pelvic-fin insertion to anal fin origin and around the anal fin totally naked. Abdomen covered by minute platelets, bearing at most six odontodes (frequently about three), scattered between posterior margin of lower lip and insertion of pelvic fin; sometimes concentrated in central area of abdomen.

Head broad and depressed. Anterior profile of head slightly triangular to roundish in dorsal view, more rounded in mature males. Three slightly elevated ridges between orbits and snout tip, lateral ridges more prominent. Dorsal region between orbits concave; upper margin of the orbit slightly elevated; supraoccipital dorsal surface strongly convex, with an area without odontodes at the center. Eye moderately small dorsolaterally placed. Iris with minute dorsal flap covering pupil. Margins of head covered by minute odontodes; mature males with thin flesh lobes and short hypertrophied odontodes along the lateral margin of head. Lips roundish and well developed, occupying most of ventral surface of head. Lower lip reaching pectoral girdle and covered by minute papillae, which decrease in size towards its edge. Papillate surface of lower lip projecting between dentary and premaxillary rami. Maxillary barbel short, coalesced with lower lip and ornamented with small papillae. Teeth small and bicuspid, inner cusp slightly curved inwards. Lateral cusp small, not reaching half-length of inner cusp (three times shorter than inner cusp).

Cleithrum not exposed, or partially exposed only bordering the ventral margin of pterotic-supracleithrum. Region below the three initial plates of the lateral line (just posterior to the pterotic-supracleithrum) nude.

Dorsal fin originating on vertical line passing through pelvic-fin origin, and finishing on vertical line passing through anal-fin origin; nuchal plate present, spinelet and locking mechanism absent. Dorsal-fin spine moderately flexible. Adipose fin present, preceded by one or two median, unpaired pre-adipose azygous plates. Pectoral fin moderate in size; with curved and depressed spine, which have a short extension of skin on its tip; spine covered with short hypertrophied odontodes, mainly on its lateral and ventral surface; dorsal surface with discrete dermal flap along its entire length. First and second branched rays as long as the spine. Subsequent branched rays reduced gradually in size, last ray less than half length of first one. Posterior margin of pectoral fin straight, overlapping approximately half-length of pelvic fin when adpressed. Pelvic fin moderate in size, not reaching insertion of anal fin when adpressed. Pelvic-fin spine depressed, covered with minute odontodes ventrally and laterally; well developed dermal flap on its dorsal surface, extending to spine tip. Anal fin with the first ray unbranched. Distal profile of caudal fin concave, but some mature specimens presented it straight; lower lobe slightly longer than upper.

Color in alcohol. Ground color of upper surface of head and body grayish or dark brown; pale yellow ventrally. Dorsum and flanks mostly plain but sometimes with dark brown blotches of various sizes and shapes, associated with lighter blotches irregularly arranged. Dorsal light blotches sometimes arranged to form four inconspicuous saddles on dorsum: on origin of dorsal fin, on posterior portion of dorsal-fin base, between end of dorsal-fin and adipose fin, and between adipose and caudal fins. A lighter vertical thin blotch on the lateral side in the end of caudal peduncle, sometimes not continuous. Ventral margin of head, outer portion of upper lip, and ventral portion of caudal peduncle dusky. Ventral surface unpigmented between head and anal-fin origin. Spines of dorsal, pectoral, pelvic, anal and caudal fins grayish or with four to six dark spots; branched fin-rays with two to four dark brown spots, forming transverse stripes; interradial membrane of fins hyaline.

Distribution. This species is only known from córrego Juruba and ribeirão Água dos Oito, affluents of rio Taquara, rio Tibagi basin, Paraná State, Brazil (Fig. 4).

Etymology. The species name calvus, a Latin adjective, means bald, in allusion to the area on the head, without odontodes.

Ecological notes. The type locality where some specimens of Isbrueckerichthys calvus were collected is a small creek of rural region, flowing through a landscape of mixed open field, riparian vegetation and forest, sometimes with a very degraded margin. Grass or other vegetation is usually present on the margins. The stretch sampled is narrow (about 2-4 m wide) and shallow (about 0.2-0.5 m deep). The stream bottom was rocky, with small to medium-sized rocks, loose stones and gravel; and some small pools along the stream with sand and mud on the bottom. The water was clear to turbid and moderate to fast flowing. The fishes were usually found along the bottom among rocks and stones, just under small waterfalls.

The following species occur syntopically with Isbrueckerichthys calvus : Hypostomus ancistroides (Ihering) , Neoplecostomus sp. and Rineloricaria pentamaculata Langeani & Araujo .

Comments. Another character that also helps to distinguish both species herein described is the greater number of plates in the following counts of Isbrueckerichthys saxicola : median plate series, dorsal plates below dorsal-fin base, plates between end of dorsal-fin base and adipose fin, and ventral plates between end of anal-fin base and caudal fin (Table 1). On the other hand, Isbrueckerichthys calvus has a more robust body, with plates more evenly spaced covering the dorsal surface of the body.