Mastiglanis durantoni from French Guyana, a second species in the genus (Siluriformes: Heptapteridae), with a CT scan survey of phylogenetically-relevant characters

A new species of the heptapterid genus Mastiglanis, M. durantoni, is described from three adjacent localities in the upper reaches of the Maroni River in French Guyana. The new species is distinguished from the only other known species in the genus, M. asopos, by several qualitative and quantitative characteristics, such as the slender caudal peduncle (caudal peduncle depth 4.3-5.3% of SL vs. 5.6-6.3%); the upper jaw protruding markedly beyond lower, resulting in long snout (36.5-42.0% of HL vs. 23.4-33.6%); the head depressed (head depth 34.0-44.4% of HL vs. 44.4-53.0%); the procurrent caudal fin rays 12 dorsally and ventrally (vs. 14-17); the dorsal margin of adipose fin concave (vs. variably convex, straight or gently sinusoidal); the occipital process deeply notched, distally V-shaped (vs. distal margin of occipital process variably-shaped, with notch, when present, not deep and forming an obtuse angle); the mesethmoid cornu widest at its midlength (vs. gradually narrower from base to tip). Characters of taxonomic and phylogenetic relevance are observed and illustrated with CT-scan imaging technique. The narrowly endemic and outlying geographical distribution of the new species contrasts with the extremely wide range of M. asopos and suggests a history of peripheral isolation and differentiation. In conformity with that interpretation, the new species has some autapomorphic specializations, while none is currently known for M. asopos.