Abstract
The ariid catfish Plicofollis dussumieri (Valenciennes) is redescribed in detail based on examination of the holotype and additional material from the Indian Ocean. Part of the material examined herein was collected by bottom trawl from sandy bottoms off Jizan, Saudi Arabia, and represents the first record of the species for the Red Sea. Plicofollis dussumieri is characterised in having 14-18 anal-fin rays; two pairs of palatal tooth plates bearing granular teeth; parietosupraoccipital process rhomboidal or oblong with straight lateral sides and usually emarginate apex; lateral ethmoid globular, prominent; anal-fin height 8.2-12.4% SL; and adipose fin dark distally. Examination of specimens exhibited sexual dimorphism in the species with greater predorsal distance, longer pelvic fins and pelvic-fin base in females. Ontogenetic changes were found in several characters: length of maxillary and mental barbels, anal-fin base, and adipose-fin base are becoming shorter and eye diameter smaller with growth. In addition to the detailed study of a representative number of specimens of P. dussumieri, the present study provides an identification key to the species of the genus, and a phylogenetic analysis of available mitochondrial gene sequences (cyt b and ATPase 8/6), including species not considered in previous molecular studies.