The Pharyngeal Bones and Teeth of Catostomid Fishes

Abstract

Examination of the pharyngeal apparatus of 22 spp. of catostomids reveals 3 types of bones and teeth associated with different dietary habits. The mollusk feeders Moxostoma hubbsi and M. carinatum have 21-42 large, molariform teeth on each of the heavy pharyngeal bones. The teeth occlude with a chewing pad borne by the basioccipital and are well-adapted for crushing shells. Most catostomids (other Moxostoma, Cycleptus, Hypentelium, Lagochila, Catostomus, Chasmistes, Erimyzon, Xyrauchen and Minytrema) have 43-90 moderately compressed teeth arranged in comblike fashion on each bone. These species feed primarily on benthic macroinvertebrates including aquatic insect larvae and small mollusks. In addition to mastication, the teeth of this group probably serve to manipulate and hold food during the rejection of inorganic matter inadvertently taken in with the food. The teeth of Ictiobus and Carpiodes are extremely small and numerous (134-184), and the pharyngeal bones are correspondingly delicate. These species are microphagous filter feeders with a well-developed selectory apparatus consisting of gill rakers, gill arches and palatal organ. The teeth are capable of masticating small food items and may also function as strainers. An analytical key based only on pharyngeal bone and tooth characteristics is provided, and the bones and teeth of several species are illustrated. Catostomid pharyngeal bones and teeth have some limited use in specimen identification. They are usually reliable at the tribe or genus level. In certain trophically specialized forms (M. hubbsi, M. carinatum and I. cyprinellus) they are significant at the species level.