A STUDY OF THE TEMPORARY ADHESION OF THE PODIA IN THE SEA STAR ASTERIAS-RUBENS (ECHINODERMATA, ASTEROIDEA) THROUGH THEIR FOOTPRINTS

Sea stars are able to make firm but temporary attachments to various s ubstrata owing to secretions released by their podia, A duo-glandular model has been proposed in which an adhesive material is released by t wo types of non-ciliated secretory (NCS1 and NCS2) cells and a de-adhe sive material is released by ciliated secretory (CS) cells. The chemic al composition of these materials and the way in which they function h ave been investigated by studying the adhesive footprints left by the asteroids each time they adhere to a substratum, The footprints of Ast erias rubens consist of a sponge-like material deposited as a thin lay er on the substratum, Inorganic residues apart, this material is made up mainly of proteins and carbohydrates. The protein moiety contains s ignificant amounts of both charged (especially acidic) and uncharged p olar residues as well as half-cystine. The carbohydrate moiety is also acidic, comprising both uronic acids and sulphate groups. Polyclonal antibodies have been raised against footprint material and were used t o locate the origin of footprint constituents in the podia. Extensive immunoreactivity was detected in the secretory granules of both NCS1 a nd NCS2 cells, suggesting that their secretions together make up the b ulk of the adhesive material. No immunoreactivity was detected in the secretory granules of CS cells, and the only other structure strongly labelled was the outermost layer of the cuticle, the fuzzy coat. This pattern of immunoreactivity suggests that the secretions of CS cells a re not incorporated into the footprints, but instead might function to jettison the fuzzy coat, thereby allowing the podium to detach.