Redescription of the Guiana Shield Darter Species Characidium crandellii and C. declivirostre (Crenuchidae) with Descriptions of Two New Species

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.

Range extension of the miniature pencil‐catfish Potamoglanis wapixana (Siluriformes: Trichomycteridae) into the Essequibo River basin, Guyana

“…This drainagethe proto-Berbicedrained the southern slope of the western Guiana Shield into the northern Atlantic Coast of South America (Lujan & Armbruster, 2011). The proto-Berbice has been invoked to explain distributions of various rheophilic fish species occurring in headwaters of the Orinoco, the upper Branco and/or throughout the Essequibo, whose occurrences on opposite sides of the modern Rupununi Savannahs are hypothesized to be relicts of a once-contiguous distribution throughout the proto-Berbice (e.g., Armbruster et al, 2021). This provides one possible hypothesis to , 2019Lovejoy & De Araújo, 2000;Sabaj et al, 2020;Willis et al, 2012).…”

New Species of Trichomycterus (Siluriformes: Trichomycteridae) from Wetlands of High Elevation of Argentina, with Notes on the T. alterus Species-Complex

“…Juveniles of T. puna were observed almost entirely in the absence of water currents and in shallow waters along marginal standing waters, areas normally avoided by juveniles and adults. Benthic, rheophilic fishes have many adaptations to maintain position in swift currents, such as ventral pads of tissue that help to resist abrasion and increase adhesion via microscopic keratinous structures known as unculi (Lujan and Conway, 2015; Bressman et al, 2020; Armbruster et al, 2021). Trichomycterus puna shows thickening of the epidermis on ventral head and fleshy lower lip that generates downforce from water flowing over them.…”