Comparison of the oral cavity architecture in surgeonfishes (Acanthuridae, Teleostei), with emphasis on the taste buds and jaw retention plates

The present study summarizes observations on the skin plates (retention plates) and taste buds (TBs) in the oropharyngeal cavity (OC) of 15 species of surgeonfishes (Acanthuridae), all of which are predominantly herbivorous. Two phenomena mark the OC of these fishes: the presence of skin-plates rich in collagen bundles at the apex of the jaws, and cornified papillae on the surface. It is suggested that these plates help in retaining the sections of algae perforated at their base by the fishe's denticulate teeth. The TBs, especially type I, are distributed across the buccal valves, palate and floor of the OC, forming species-specific groupings along ridges established by the network of sensory nerves. The number of TBs in the OC increases with growth of the fish up to a certain standard length, especially at the posterior part of the OC, and differs among the various species: e. g., Zebrasoma veliferum possesses 1420 TBs and Parcanthurus hepatus 3410. Species of Naso show a higher number of TBs than most species of Acanthurus, possibly connected with their more diversified diet. The pharyngeal region of these fishes is expanded through lowering the base of the gill-arches, and together with the occurrence of high numbers of TBs in this region, indicates the importance of the posterior region of the OC in herbivorous fishes for identification of the engulfed food particles prior to swallowing. The discussed observations shed light on the micro-evolutionary developments of the OC within the family Acanthuridae and contribute to the taxonomic characterization of the various species.