Lithoxus jantjae, Lujan, 2008

Lujan, Nathan K., 2008, Description of a new Lithoxus (Siluriformes: Loricariidae) from the Guayana Highlands with a discussion of Guiana Shield biogeography, Neotropical Ichthyology 6 (3), pp. 413-418 : 414-415

Lithoxus jantjae , new species

Fig. 1

Holotype. MCNG 55349 , 38.4 mm SL, Venezuela, Amazonas, río Ventuari, above Tencua Falls 58 km ESE of San Juan de Manapiare, approx. 5º2’N, 65º36’W, 21 Apr 2004, N. K. Lujan, O. León, A. Luna & A. Yarumare.

Paratypes. Same data as holotype . ANSP 182809 , 4 , 21.4-33.7 mm SL (2, 30.6, 33.7 mm SL) ; AUM 39478, 4 , 21.6-32.3 mm SL (1, 32.3 mm SL) ; MCNG 55350 , 2 , 22.1 , 29.0 mm SL (1, 29.0 mm SL) .

Diagnosis. Lithoxus jantjae can be separated from all other Lithoxus by having 12 branched caudal-fin rays (vs. 14); from all Lithoxus except L. lithoides by having four branched analfin rays (vs. five), and five interdorsal plates (vs. six to eight when adipose fin present); from all Lithoxus except L. lithoides and L. stocki by having a convex posterior membranous extension of the adipose fin (vs. adipose fin, when present, without posterior extension, posterior margin strait or concave); from all Lithoxus except L. lithoides and L. bovallii by having medial premaxillary teeth with an enlarged and widened cusp (vs. cusps of all premaxillary teeth similar in size, not enlarged); from all Lithoxus except L. lithoides , L. stocki and L. boujardi by having an obliquely truncate to slightly emarginate caudal fin (vs. caudal fin obliquely forked with a distinct upper caudal lobe); from L. lithoides by having a mode of 24 supramedian plates (vs. mode of 25) and a mode of 18 (range 16-25) hypertrophied cheek odontodes (vs. mode of 12, range five to 21); and from L. pallidimaculatus and L. surinamensis by having an adipose fin (vs. adipose fin absent).

Description. Morphometrics in Table 1. Largest specimen 38.4 mm SL. Body dorsoventrally depressed; dorsal profile strongly convex from anterior tip of upper lip to nares, distinctly curved near snout tip; slightly convex from nares to dorsal-fin origin; nearly straight from latter point to adipose-fin origin and distinctly concave from latter point to caudal fin. Ventral profile somewhat straight from snout tip to caudal fin. Ventral profile flat to caudal fin. Caudal peduncle approximately triangular in cross section, with dorsal surface and ventrolateral corners rounded. Body widest at insertion of pectoral fins, narrowest at insertion of caudal fin. Snout rounded in dorsal view.

Eyes small, iris operculum absent. Interorbital surface flat with modest lateral rise at supraorbital crests. Supraoccipital not elevated. Odontodes along lateral margin of opercle enlarged.

Oral disk occupying entire ventral surface of head. Ventral surface of disk covered with low, wide papillae; margin of disk fringed with low triangular papillae. Maxillary barbel short and projecting laterally or somewhat anterolaterally from anterolateral corners of upper lip.

Median plates 24-25 (mode 24). Plates not keeled. Five caudal peduncle plate rows. Five interdorsal plates. Ventrum from anteroventral margin of snout to anus without plates. Evertible cheek plates supporting hypertrophied odontodes; odontodes evertible to approximately 90º from longitudinal body axis. Hypertrophied cheek odontodes 16-25 (mode 18). Longest evertible cheek odontode extending slightly beyond anterior margin of cleithrum. Enlarged odontodes also present along anterodorsal surface of pectoral-fin spine, increasing in length distally.

Dorsal fin II,7; dorsal-fin spinelet V-shaped, dorsal-fin locking mechanism present, dorsal-fin origin approximately equidistant from snout and insertion of dorsal spine of caudal fin, dorsal fin not contacting adipose spine when adpressed. Adipose fin with single azygous preadipose plate, adiposefin membrane extending posteriorly beyond adipose-fin spine as a free flap with convex posterior margin. Caudal fin I,12,I; caudal fin obliquely truncate to slightly emarginate, lower lobe longer than upper, dorsal procurrent caudal rays four, ventral procurrent caudal rays three. Pectoral fin I,6; pectoralfin spine reaching slightly beyond base of pelvic-fin spine when adpressed dorsal to pelvic fin. Pelvic fin I,5; pelvic-fin spine reaching slightly beyond base of anal fin when adpressed. Fin rays of dorsal, caudal, pectoral and pelvic fins extending beyond fin membranes to form fimbriate posterior margins.Anal fin i,4. Anal papilla distinct.

Teeth bicuspid with deep division between cusps; two to five left premaxillary teeth (mode five), four to eight left dentary teeth (mode five); premaxillary tooth cusps increasing in size from lateralmost tooth to medialmost tooth with medialmost tooth cusp two to four times as large as lateralmost tooth cusp, lateralmost premaxillary tooth cusps similar in size to dentary tooth cusps.

Color in alcohol. Dorsum consisting of dark brown mottling on light brown to yellow base; mottling concentrated to form four indistinct saddles in most but not all specimens; pattern extends onto rays and spines of all but the anal fin; fin membranes transparent; plates of snout accentuated by dark center with lighter edges. Ventrum including oral disk uniformly light yellow to sand-colored.

Distribution. Known only from rapids that extend for a few hundred meters upstream of Tencua Falls, the first major faunal barrier in the Ventuari River (pers. obs.), a right bank tributary of the upper Orinoco in Amazonas State, Venezuela ( Fig. 2 ).

Etymology. Matronym honoring the author’s mother, nicknamed Jantje prior to her emigration from the Netherlands, in deep appreciation for her hard work and material and emotional encouragement that promoted his professional development and made this research possible. Pronounced yäntchi.

Figures

Fig.1. Lithoxusjantjae, holotype,MCNG 55349, 38.4mm SL,Venezuela,Amazonas State,Ventuari River upstream ofTencua Falls.

Fig. 2. Distribution of Lithoxus jantjae (filled circle) and L. lithoides (open circles), the geographically closest described species of Lithoxus.