Hemiodus jatuarana, Francisco Langeani, 2004

Francisco Langeani, 2004, Hemiodus jatuarana, a new species of Hemiodontidae from the rio Trombetas, Amazon Basin, Brazil (Teleostei, Characiformes)., Zootaxa 546, pp. 1-6 : 2-4

Hemiodus jatuarana n. sp.

Fig. 1

Type material. Brazil, State of Pará, rio Trombetas: Oriximina , Feb-Mar 1967, Expedição Permanente à Amazônia (EPA) leg.; MZUSP 54083 , holotype, 192 mm SL; MZUSP 83358 , 2, 193-195 mm SL, paratypes.

Diagnosis. Hemiodus jatuarana is readily distinguished from its congeners by the horizontally elongated dark spot on the caudal peduncle, and no other conspicuous dark pigmentation pattern, as those present in other Hemiodus species (e.g. round midlateral body spot in most Hemiodus species, vertical bars in H. quadrimaculatus species group , or longitudinal stripe of H. ternetzi Myers , 1927, H. thayeria Boehlke , 1955, and H. tocantinensis Langeani , 1999). Furthermore, it is separated firom H. immaculatus , the most similar species, by having 25-27 epibranchial and 36-37 ceratobranchial gill rakers on first branchial arch (vs 14-16 and 21-25 in H. immaculatus ), and caudal-fin lobes without longitudinal stripes (vs conspicuous longitudinal stripe on each caudal-fin lobe in H. immaculatus ).

Description. Morphometric and meristic data are shown on Table 1. Medium size, 192 to 195 mm SL. Greatest body depth at dorsal-fin origin. Dorsal profile straight or slightly convex along head and predorsal portion, straight and descendent along dorsal-fin base, convex along post-dorsal portion and concave at caudal peduncle. Ventral profile convex from head to pelvic-fin base, straight or slightly convex along post-pelvic portion, convex at anal-fin base, and concave at caudal peduncle.

Head profile anteriorly pointed; interorbital region convex, equal to snout length, and greater than orbital diameter. Mouth slightly sub-terminal. Upper jaw not protractile with multicuspidate teeth with convex border. Lower jaw edentulous, rounded anteriorly. Adipose eyelid well developed, covering eye entirely, except for vertically elongate opening overlying pupil. Gill rakers triangular, posterior ones longer than the anterior, with small ctenii along adpharyngeal border; 25-27 epibranchial and 36-37 ceratobranchial gill rakers on first branchial arch.

Medium size (about three times in the eye diameter), thin, cycloid scales over entire body. Lateral-line scales from supracleithrum onto caudal-fin base 66 to 72 (68.3). Scales above lateral line in transverse series to dorsal-fin origin 12 or 13 (12.3); scales below lateral line in transverse series to pelvic-fin origin 6 or 7 (6.3). Cleithrum followed by 5 or 6 horizontally elongated scales forming small elevation above axillar depression, into which proximal end of first pectoral ray fits, in depressed fin. Axillary process of pelvic fin formed by three scales, last scale greatly elongated.

Dorsal fin ii + 9, last ray sometimes branched at base. Adipose fin about same size as orbital diameter. Pectoral fin i + 19 to 21 (i + 20), extending little beyond middle point between its base and pelvic-fin insertion. Pelvic-fin rays i + 11, extending beyond anal-fin origin. Anal fin ii + 8 to 10 (ii + 8.7), its posterior border slightly concave. Caudal fin 10 + 9; with lobes equal.

Color in alcohol. Relatively small, horizontally elongate spot of dark pigmentation present on caudal peduncle; no other conspicuous body markings (e.g. midlateral spot, vertical bands or horizontal stripe) present. Central portion of scales above lateral line peppered with small brown chromatophores. Dorsal, pectoral, pelvic, and anal fins hyaline; caudal-fin rays light brown.

Distribution. Known only from type-locality: Rio Trombetas, at Oriximiná, Pará, Brazil(fig. 2).

Etymology. The species name, jatuarana, is vernacular Portuguese word, derived from the Tupi-Guarani, applied to most of species of Hemiodus species in the Brazilian Amazon. A noun in apposition.

Comments. Hemiodus immaculatus and H. jatuarana have similar color pattern, body shape, and scale size, and occur in syntopy at the type locality of H. jatuarana (fig. 2).

It is interesting how rare specimens of H. jatuarana are in systematic collections. Frequently, large-size hemiodontids occur in river channels and are easy to capture, some being commercially exploited and relatively common in museum collections. Future efforts should be made around the type-locality in order to collect additional specimens of H. jatuarana .