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 southwestern Ross Sea was studied for intraspecific variation in the number of second dorsal and anal rays, number of vertebrae, and length and shape of the mental barbel - a key diagnostic and taxonomic character in this family. Ranges for meristics are compact and extend documented values to 13 for anal rays and 37 for vertebrae. There is a nearly twofold difference in the relative length of the mental barbel. There are no significant differences between the sexes in any meristic or morphometric feature. The terminal expansion of the barbel exhibits four types, documented with illustrations and histology: 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-five percent of specimens have the epidermis of the terminal expansion arranged as broad ridges or mounds. The mental barbel of D. longedorsalis is therefore individually variable with no evidence of sexual dimorphism, and the type of barbel does not vary ontogenetically. Histological analysis of the barbel reveals that the terminal expansion consists of a thick epidermis and that dermal papillae are responsible for the pattern of surface projections sometimes present. The epidermis near the tip of the barbel is twofold thicker in specimens with a terminal expansion. The distal morphology of the barbel, whether straight or expanded, probably has little functional significance. The barbel is richly supplied with nerves and blood vessels and the core consists of pseudocartilage. The barbel is probably a somatosensory organ.