Abstract
Based on collections made in the western Guiana Shield over the last 21 years, Characidium crandellii and C. declivirostre are redescribed and two similar species are described from Guyana. These species all have enlarged paired fins with three to four rays thickened ventrally on the pectoral fin and two rays thickened on the pelvic fin. The species can be separated from all other Characidium and Melanocharacidium by having the venter unscaled from the isthmus to the pelvic origin. Characidium crandellii is found in the Essequibo and Takutu River systems and in an isolated population above Tencua Falls in the Ventuari River and the upper Paragua River (Orinoco River basin). Characidium declivirostre is found throughout the right-bank, shield tributaries of the Orinoco River system and in the upper Negro River. Characidium duplicatum, new species, appears to be rare but widely distributed in the Essequibo River system. Characidium wangyapoik, new species, is only known from the upper Ireng River, Branco River basin, along the border between Brazil and Guyana.
Highlights
C HARACIDIUM is the most species-rich genus (70 species, Fricke et al, 2019) in the South American darter family Crenuchidae (Characiformes); it consists of small, benthic fishes found in rivers and streams throughout most of tropical South America and southern Panama
After nearly two decades collecting in rivers of the western Guiana Shield in Venezuela and Guyana, we have amassed over 300 specimens assignable to C. crandellii, C. declivirostre, and two undescribed, similar species, providing the justification and basis for this first taxonomic revision of the rheophilic Characidium of the Guiana Shield
We initially identified four morphotypes based on a combination of color pattern, meristics, and fin positions: one containing primary types and topotypes of C. declivirostre, one that was similar to type material of C. crandellii, one from the upper Ireng River that did not match any described species, and one that was patchily distributed throughout the Essequibo River system that did not match any described species
Summary
C HARACIDIUM is the most species-rich genus (70 species, Fricke et al, 2019) in the South American darter family Crenuchidae (Characiformes); it consists of small (generally less than 8 cm SL; a 10.7 cm specimen is described here), benthic fishes found in rivers and streams throughout most of tropical South America and southern Panama. The most extensive phylogenetic analysis of Characidium was Buckup (1993a), who developed a matrix of 64 morphological characters observed across a broad diversity of Characidium and its relatives. His analysis of this matrix found support for a clade comprising Characidium crandellii and C. declivirostre (Clade C3), both of which were described by Steindachner (1915). The sister relationship between these species was supported by three unique and two homoplastic synapomorphies: 1) scaleless area of isthmus extending posteroventrally between pectoral fins to pelvics (unique); 2) branchiostegal membranes united across the isthmus (unique); 3) dermal flaps around anterior and posterior nares independent but touching each other distally (unique); 4) posterior process of coracoid reduced to squarish protuberance (homoplastic); 5) basicaudal spot secondarily absent (homoplastic). After nearly two decades collecting in rivers of the western Guiana Shield in Venezuela and Guyana, we have amassed over 300 specimens assignable to C. crandellii, C. declivirostre, and two undescribed, similar species (from the Ireng and Essequibo River basins), providing the justification and basis for this first taxonomic revision of the rheophilic Characidium of the Guiana Shield
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
