Morphological Variation of the Palatal Organ and Chewing Pad of Catostomidae (Teleostei: Cypriniformes)

We studied the morphology and shape variation of the palatal organ and chewing pad of sucker fishes, family Catostomidae. The palatal organ is a muscularized structure that forms a large mass on the roof of the posterior part of the buccopharyngeal cavity in cypriniform fishes. It functions in coordination with the branchial arches to separate food items from inorganic debris during feeding. The palatal organ exhibits considerable variability in morphology among catostomids. It is shorter, narrower, and thinner in species of the subfamily Cycleptinae (e. g., Cycleptus elongatus) than in other catostomid subfamilies. The thickest and widest palatal organ is seen in species of the subfamily Ictiobinae (e. g., Ictiobus cyprinellus). The shape and size of the palatal organ generally varies between these extremes in species of subfamily Catostominae (e. g., Catostomus and Moxostoma species). Principal components analysis and analysis of variance has differentiated means of various palatal organ measurements for each monophyletic subfamily and tribe of Catostomidae with statistical significance. These results corroborate previously established typological classification of catostomids based on pharyngeal tooth count, pharyngeal tooth morphology, and diet. A keratinized chewing pad forms on the posterior surface of the palatal organ in catostomids or on a skeletal process in cyprinids and serves as an occlusion surface for pharyngeal teeth. The chewing pad is lunate in catostomids and generally ovoid in cyprinids. It is absent from the species of loaches (e. g., botiids, cobitids, and nemacheilids) and gyrinocheilids examined. A synonymy of terms used in the past to describe the palatal organ and chewing pad of Cypriniformes is provided. J. Morphol. 272: 1092-1108, 2011. (C) 2011 Wiley-Liss, Inc.