Mental barbel and meristic variation in the Antarctic notothenioid fish Dolloidraco longedorsalis (Perciformes : Artedidraconidae) from the Ross Sea

A collection of 58 specimens of Dolloidraco longedorsalis from the southwes tern Ross Sea was studied for intraspecific variation in the number of seco nd dorsal and anal rays, number of vertebrae, and length and shape of the m ental barbel - a key diagnostic and taxonomic character in this family. Ran ges for meristics are compact and extend documented values to 13 for anal r ays and 37 for vertebrae. There is a nearly twofold difference in the relat ive length of the mental barbel. There are no significant differences betwe en the sexes in any meristic or morphometric feature. The terminal expansio n of the barbel exhibits four types, documented with illustrations and hist ology: typical expanded form (43%), not expanded or tapered (33%), slightly expanded (22%), and large expansion (2%). There is no relationship between absolute and relative barbel length and sex or barbel type and sex. There is no relationship between barbel type and size of the specimen. Twenty-fiv e percent of specimens have the epidermis of the terminal expansion arrange d as broad ridges or mounds. The mental barbel of D. longedorsalis is there fore individually variable with no evidence of sexual dimorphism, and the t ype of barbel does not vary ontogenetically. Histological analysis of the b arbel reveals that the terminal expansion consists of a thick epidermis and that dermal papillae are responsible for the pattern of surface projection s sometimes present. The epidermis near the tip of the barbel is twofold th icker in specimens with a terminal expansion. The distal morphology of the barbel, whether straight or expanded, probably has little functional signif icance. The barbel is richly supplied with nerves and blood vessels and the core consists of pseudocartilage. The barbel is probably a somatosensory o rgan.