The Respiratory Adaptations of the Podia and Ampullae of Echinoids (Echinodermata)

The morphology of the podia and ampullae of thirty echinoids spread over 7 orders is described. 2. Four adaptations for respiration are found in the podia and ampullae of echinoids. The first is the separation of ciliary currents in the podium-ampulla lumen by two pores in the body wall, a septum in some podia, and the ampulla's flattened shape. The ampullae are crossed by septae. 3. The second respiratory adaptation is an increase in surface area of ampullae and podia by flattening. Cidarids, arbacids, and spatangoids further increase podial surface area by folding. 4. The ciliary currents inside and outside of ampullae and some podia move in a counter-current, increasing respiratory efficiency. 5. The fourth adaptation for respiration is that all podia having the first three adaptations are favorably positioned on the animal for respiration. Ampullae adapted for respiration serve podia adapted for respiration. 6. All strands and septae crossing echinoid podial or ampullar lumina contain strands of connective tissue. 7. Mortensen's (1928-1951) classification most nearly predicts the podial affinities found.