Individuals of Asterias rubens and Marthasterias glacialis use their podia in locomotion and anchorage, and to open the bivalve mollusks on which they feed (Lawrence, 1987).
Paine (1926), who studied the podia of Asterias vulgaris, concluded that 56% of podial attachment would be contributed by suction and the rest by adhesive secretions.
Data presented in this report support this second hypothesis: first, many epidermal secretory cells cover the entire apical surface of the disk; second, the footprints are completely (or almost completely) full of adhesive material; and third, podia may adhere strongly with only the margin of their disk (leaving crescent-shaped footprints).
Such cells have already been observed in the podia of paxillosid asteroids, which end not with a disk, but with a conical tip (Engster and Brown, 1972); in ophiuroid podia (Ball and Jangoux, 1990); and in the locomotory podia of several holothuroid species (Harrison, 1968; Flammang and Jangoux, 1992).
CS cells are remarkably similar in all echinoderm species whose podia have been examined.
These cells, like CS cells, are almost identical in the podia of all echinoderm species studied so far (Engster and Brown, 1972; Burke, 1980; McKenzie, 1987; Ball and Jangoux, 1990; Flammang et al.
A model for the adhesive mechanism of sea star podia
We consider the two types of NCS cells to be adhesive because they are the only secretory cells having extruded some of their secretory granules in attached podia.