Amazonspinther, new genus

Diagnosis. Amazonspinther is diagnosed among all characid species by the autapomorphic presence of three conspicuous black blotches on the base of the dorsal, anal, and caudal fins (ch. 43; Fig. 1).

Amazonspinther is diagnosed among all genera of the Cheirodontinae by two uniquely derived characters, the anteriormost proximal radial of the anal fin with an anteriorly extended lamina entering the abdominal cavity, between the distal portions of the 12th to 14th pleural ribs (ch. 44; Fig. 2) (vs. short anteriorly extended lamina, not entering the abdominal cavity and not between pleural ribs), and by the extremely elongate caudal peduncle, corresponding to 27.3-30.2% of SL. Caudal peduncle length is comparatively short in cheirodontines, ranging from 11.0 to 19.6% of SL. Spintherobolus papilliferus has an elongate caudal peduncle (21.3-27.0% of SL), but shorter than that observed for Amazonspinther .

Among all genera of the tribe Cheirodontini, Amazonspinther is diagnosed by two features: a small number of ventral procurrent caudal-fin rays (7-9 vs. 11-28; Malabarba, 1998: 205-207, 209, ch. 42; Weitzman & Malabarba, 1999:8-9, ch. 5; 11-16 in Spintherobolus species) (Fig. 3); and hemal spines of one, two, or sometimes three posterior caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays (Fig. 3; vs. hemal spines of at least the four posterior caudal vertebrae directly articulating with the ventral procurrent caudal-fin rays).

Etymology. Amazon, in reference to the Amazon basin, and spinther from the Greek spinther, masculine, meaning sparks, fire, in reference to both the closely related genus Spintherobolus and to the appearance of the yellow neuromasts of the head, also observed in Spintherobolus (Fig. 4).