The Unusual Mental Barbel of Antarctic «Cryonotothenioid» Fishes of the Subfamily Artedidraconinae: Morphology, Variability and Function

The single mental barbel is a distinctive feature of the benthic Antarctic fishes of the «cryonotothenioid» subfamily Artedidraconinae. These barbels are unusual because their primary sensory modality is tactility, not chemosensation as in most other teleosts. They also exhibit considerable interspecific and intraspecific variation in length and in the appearance of the terminal expansion and its epidermis. Barbels range from short to long and the terminal expansion can be nonexistent, small and round, or large and oblong. In most species, the epidermal surface of the terminal expansion exhibits projections of various shapes and sizes. These range from smooth and furrowed, to ridged and furrowed, to pointed, to palmate (having lobes originating from a common point), and to fringed and leaf-like. Barbels are also subject to intraspecific variation among the species in the genera Dolloidraco, Histiodraco, Artedidraco and Pogonophryne. The various epidermal surface patterns all increase the sensory surface area exposed to the substrate and may enhance detection of their prey, primarily polychaetes. They also enhance surface roughness of the epidermis, thereby dissipating mechanical forces and providing some protection from abrasion by the substrate. The various patterns are likely an epigenetic response to different local conditions of the substrate. This variation warrants caution in their use as a defining taxonomic character.