A remarkable new Characidium (Characiformes: Crenuchidae) from tributaries of río Marañón, Loreto, Peru, with unique fin bony processes in both sexes

Abstract A new species of Characidium from tributaries of the río Marañón, Loreto, Peru is described.The new species is promptly distinguished from congeners and also remaining species of Crenuchidae by two exclusive features: females and males with bony processes along length of the pectoral-fin rays, including immature and mature specimens, and paired fins with black longitudinal bands that extend along the total length of a few unbranched and branched rays. The species is further differentiated from most congeners, with the exception of some psammophilous species, by the presence of strongly tricuspid teeth on the premaxilla and dentary, with three well developed and similar sized cusps, and a black dashed midventral line extending from area between pectoral fins to caudal peduncle. Characidium sp. n. is externally similar to psammophilous species such as C. fleurdelis and C. pteroides, but a definition of its relationships depends on future comprehensive phylogenetic studies of Characidium.