Morphology and function of the feeding apparatus of Pelusios castaneus (Chelonia; Pleurodira).

Feeding mechanics of vertebrates depend on physical constraints of the surrounding media, water or air. Such functions are inseparably combined with form. The aim of this study is to show this linkage for the pleurodiran freshwater turtle Pelusios castaneus and, additionally, to point out the major functional and biomechanical distinctions between aquatic and terrestrial feeding turtles as well as several intermediate forms. Gross morphological investigations of skull, hyoid, tongue, and connected musculature, as well as scanning electron microscopy of the tongue surface, show typical features of an aquatic feeder, e.g., strongly developed hyoid apparatus vs. a small tongue with only moderate papillae, and massive jaw and hyoid musculature. Additionally, the special function of the esophagus during feeding is investigated to elucidate the problems of a bidirectional feeder. The esophagus is highly distensible in order to store the excess water sucked in during feeding until the prey is fixed by the jaws. The distension is probably achieved by a coincidence of active (branchial horn) as well as passive (water) components. P. castaneus is a feeding generalist, and is well adapted to the aquatic medium in terms of its functional as well as morphological features. Copyright 2000 Wiley-Liss, Inc.