Pimelodella humeralis

description

Description. Measurements in Table 1. Body of moderate height, depth at dorsal-fin origin five times or more in standard length, and compressed, body width at dorsal-fin origin not exceeding half of head length (Fig. 1). Greatest body depth at dorsal-fin origin. Dorsal profile straight from snout to dorsal-fin origin; slightly concave from that point to adipose-fin origin. Profile slightly convex along adipose fin base, and concave along caudal peduncle. Ventral profile of body slightly convex from snout to posterior limit of branchiostegal membrane, convex between branchiostegal membrane and pelvic-fin origin, slightly concave from the latter to anal-fin origin, and broadly concave from that point to caudal insertion. Pseudotympanum large, oval, dorsal to posterior process of cleithrum and reaching 6 th vertebrae (6). Posterior process of cleithrum triangular, its dorsal border straight to slightly concave. Axillary pore present at pectoral-fin base. Anus and urogenital papilla adjacent. Urogenital papilla short, triangular and tubular. Head deep, depth at supraoccipital-process base half of head length. Mouth subterminal. Eye slightly elliptical, its greatest diameter along horiz

A new species of Pimelodella (Siluriformes: Heptapteridae) from the Guiana Shield, Brazil

description

Pimelodella sp. — Aleixo et al., 2011: 20 [in list of species].

A new species of Pimelodella (Siluriformes: Heptapteridae) from the Guiana Shield, Brazil

diagnosis

Diagnosis. Pimelodella humeralis differs from all congeners by having a dark anteriorly oblique blotch in the humeral region (Fig. 1), its anterior limit slightly ahead of vertical through the spinelet, and its posterior limit at vertical through the base of second branched dorsal-fin ray. Moreover, P. humeralis differs from most congeners (except P. breviceps, P. cristata, P. dorseyi, P. gracilis, P. ophthalmica, P. parnahybae, P. steindachneri, P. taenioptera, P wesselii and P. witmeri) by having 47 to 49 total vertebrae (vs. 37 to 44 total vertebrae). Pimelodella humeralis differs from P. breviceps, P. cristata, P. dorseyi, P. gracilis, P. ophthalmica, P. parnahybae, P. steindachneri, P. taenioptera and P. wesselii by having 8 – 11 retrorse triangular, broad-based and strongly inclined dentations confined to basal three-fourths of pectoral-fin spine posterior margin (vs. 11 – 25 retrorse, narrow-base dentations along almost entire pectoral-fin spine posterior margin in P. breviceps, P. cristata, P. dorseyi, P. gracilis, P. ophthalmica, P. parhanybae, P. steindachneri, P. taenioptera and P. wesselii; condition unknown in P. witmeri), and also by the presence (vs. absence) of unpi

A new species of Pimelodella (Siluriformes: Heptapteridae) from the Guiana Shield, Brazil

distribution

Distribution and habitat. Pimelodella humeralis is only known from the Rio Ipitinga, a major right bank tributary of the Rio Jari which drains the eastern Guiana Shield into the lower Amazon (Fig. 4). The Ipitinga headwaters are located in the Colinas do Amapá geomorphological formation (approx. 300 m elevation), where it has many rapids along the main channel. The specimens were collected along a sandy beach in the middle stretch of the river (Fig. 5). Water parameters measured during the collection event were: 26.1 – 26.7 ºC; pH 4.25 – 4.46; conductivity 76 - 77 mS.

A new species of Pimelodella (Siluriformes: Heptapteridae) from the Guiana Shield, Brazil