Ontogeny of the Cypriniform Pharyngeal Jaw Apparatus and its Associated Musculature
Open AccessThe pharyngeal jaw apparatus is an assemblage of bones and muscles found within the head of fishes. While the oral jaws are used for prey capture in fishes, the pharyngeal jaws are used for prey processing. There is a basic form of the pharyngeal jaw apparatus found amongst all fishes; however, some fish groups possess features of the pharyngeal jaw apparatus that are specialized for the demands of their diet (Vandewalle, 2000). One such group are the Cypriniformes. Cypriniformes is one of the world's largest clades of freshwater fishes (Nelson, 2006). They are widely distributed in North America, Europe, Africa, and Asia, but are absent from Australia and South America. The clade is united by several characters, including the presence of a kinethmoid, a lack of teeth on the oral jaws, and an enlarged fifth ceratobranchial that opposes a pad on the basioccipital of the skull. Using developmental and histological methods, I investigated the development of the cypriniform pharyngeal jaw apparatus, a morphological novelty for this group of fishes, using the zebrafish model system. Results indicate that the zebrafish's enlarged fifth ceratobranchial is the largest ceratobranchial very early on in development. Additionally, the levator posterior, which mediates movement of this bone, is also larger than the other levators through ontogeny, beginning very early on in development. Lastly, a unique pattern of bone and muscle development was observed, where the levators externi developed prior to the appearance of the bony elements on which they attached. In contrast, the levators interni developed at approximately the same time as the bony elements on which they attach. This study is one of the first to provide insight into how the pharyngeal jaw apparatus as a whole develops.
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