THE ROLE OF PODIAL SECRETIONS IN ADHESION IN 2 SPECIES OF SEA-STARS (ECHINODERMATA)

Individuals of Asterias rubens and Marthasterias glacialis use their p odia in locomotion, anchorage, and feeding. Each podium consists of a stem with a disk at its tip. The stem allows the podium to lengthen, f lex, and retract, and the disk allows the podium to adhere to the subs tratum. Adhesion of sea star podia seems to rely on the epidermal secr etions of the disk and not on a mechanical sucker-like operation. The disk epidermis is made up of five cell types: nonciliated secretory ce lls (NCS cells) of two different types (NCS1 and NCS2), both containin g granules that are at least partly mucopolysaccharidic in composition ; ciliated secretory cells (CS cells) containing small granules of unk nown content; nonsecretory ciliated cells (NCS cells); and support cel ls. The epidermal cells of the podial disk are presumably functioning as a duogland adhesive system that is involved in an adhesive/deadhesi ve process. The following model is presented. Adhesive secretions are produced by NCS1 and NCS2 cells (both of them have extruded some of th eir secretory granules in attached podia). These secretions constitute a layer of adhesive material between the podium and the substratum, t his layer being the footprint left by the podium after it has become d etached from the substratum. Deadhesion, on the other hand, would be d ue to CS cell secretions. All these secretions would be controlled by stimuli perceived by the two types of ciliated cells (receptor cells), which presumably interact with the secretory cells via the nerve plex us.