Morphological Variation of the Palatal Organ and Chewing Pad of Catostomidae (Teleostei: Cypriniformes) Michael H. Doosey* and Henry L. Bart Jr. Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana 70118 ABSTRACT We studied the morphology and shape var- iation of the palatal organ and chewing pad of sucker fishes, family Catostomidae. The palatal organ is a mus- cularized 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 consid- erable variability in morphology among catostomids. It is shorter, narrower, and thinner in species of the sub- family Cycleptinae (e.g., Cycleptus elongatus) than in other catostomid subfamilies. The thickest and widest palatal organ is seen in species of the subfamily Ictiobi- nae (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 var- ious palatal organ measurements for each monophyletic subfamily and tribe of Catostomidae with statistical sig- nificance. These results corroborate previously estab- lished typological classification of catostomids based on pharyngeal tooth count, pharyngeal tooth morphology, and diet. A keratinized chewing pad forms on the poste- rior 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 syn- onymy of terms used in the past to describe the palatal organ and chewing pad of Cypriniformes is provided. J. Morphol. 272:1092–1108, 2011. Ó 2011 Wiley-Liss, Inc. KEY WORDS: buccopharyngeal cavity; Cyprinidae; feeding structures; pharyngeal pad INTRODUCTION The Cypriniformes are a diverse group of fresh- water fishes with 3,268 species classified in about 350 genera in nine families (Nelson, 2006; Mayden et al., 2009). The buccopharyngeal cavity is impor- tant for seizure, retention and transport of food items (Kapoor et al., 1975), and because cyprini- forms lack oral and palatal teeth, all mastication of food items occurs in the pharyngeal region (Vande- walle et al., 2000). The palatal organ (PO) is a mus- cular pad that forms the roof of the anterior phar- ynx in cypriniform fishes. Generally, it is cordate or sub-rectangular in shape, usually wider anteriorly and narrower posteriorly (Fig. 1). A histological study of the PO in the sucker, Catostomus catosto- mus, indicated that it is composed of striated mus- cle, adipose and connective tissues, and collagen fibers (Weisel, 1962). The surface is composed of stratified epithelium (Sibbing, 1986) and numerous taste buds in the carp, Cyprinus carpio. The osteo- logical structure of the PO comprises four pairs of pharyngobranchials and four pairs of epibranchials anteriorly, and the pharyngeal process of the basioc- cipital bone posteriorly (Weisel, 1960; Eastman, 1977; Sibbing and Uribe, 1985). The PO extends below from the posterior portion of the parasphenoid bone to the pharyngeal process of the basioccipital (Willink, 2002). In the cyprinid Carassius auratus, the PO begins to form at 6 mm total length and is adult-like at 9 mm (Lamb and Kiyohara, 2005). The PO functions in separating food items from inorganic debris during feeding (Sibbing, 1986; 1988; Willink, 2002). This is especially important in benthic suction feeding fishes such as catosto- mids (Willink, 2002) and some cyprinids (Osse et al., 1997; Sibbing, 1988) that intake substrate with prey, and the PO is generally larger in spe- cies of these groups. Contractions of striated muscles in the PO form localized bulges, which restrict the pharyngeal cavity except for spaces between the PO and the gill rakers (Sibbing and Uribe, 1985). The bulges of the PO pins food items against the gill rakers and then small waste par- ticles, inorganic material, and water are flushed out of the cavity through the operculums. Food items are transported to the posterior pharynx for Additional Supporting Information may be found in the online version of this article. Contract grant sponsor: National Science Foundation (Cyprini- formes Tree of Life Project); Contract grant number: EF 0431259. *Correspondence to: Michael H. Doosey, University of Kansas, Biodiversity Institute, 1345 Jayhawk Blvd, Lawrence, KS 66045. E-mail: doosey@ku.edu Received 19 July 2010; Revised 25 January 2011; Accepted 9 March 2011 Published online 19 May 2011 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/jmor.10966 JOURNAL OF MORPHOLOGY 272:1092–1108 (2011) Ó 2011 WILEY-LISS, INC.