Ultrastructure of the tube-foot of an ophiuroid echinoderm, Hemipholis elongata

The morphology of the tube-foot of the brittlestar, Hemipholis elongata was examined by transmission and scanning electron microscopy. The entire surface of the tubefoot is covered by microvilli and a thick cuticle layer. At the tip of the tube-foot the cuticle layer is thinner and sensory-secretory complexes are seen. These are composed of two secretary cells and a central ciliated sensory cell. Scanning electron microscopy shows that the cilium which extends from the receptor cell ends flush with the surrounding microvilli. These studies suggest that the tube-feet in ophiuroids are important structures in sensory-reception, gasexchange as well as locomotion. The hemoglobin containing cells within the lumen of the tubefeet may serve in oxygen transport and storage.