ULTRASTRUCTURE OF THE CILIATED CUPS OF A SYNAPTID HOLOTHUROID, LEPTOSYNAPTA-GALLIENNEI (ECHINODERMATA)

The medial epidermal surface of the buccal tentacles of the synaptid h olothuroid, Leptosynapta galliennei, bears 5-30 ciliated cups. Each cu p consists of an epidermal elevation with a central invagination formi ng a small pit. Whereas the epidermis of the outer lining of the cups is similar to that on the adjacent tentacle, the epidermis lining each pit consists of ciliated cells gathered together in a central bulb an d surrounded by elongated support cells. The basal parts of ciliated c ells are tapered and, together, form a nerve bundle entering the intra dermal nerve plexus of the tentacle. We suggest that the ciliated cell s and thus the entire ciliated cup has chemo-sensory function. It is f urther suggested that the cups allow the holothuroid to test the prope rties of the surrounding water and could also provide information on t he palatibility of collected food material.