ABSTRACT
The podia of Antedon bifida always occur in triplets. These podia bear two kinds of sensory-secretory structures, viz. papillae and hillocks. Papillae occur on the three podial types while hillocks occur only on tertiary podia. These both structures are made of a central microtubule-filled cell, neuroepithelial cells, two types of secretory cells (type 1 and type 2 secretory cells in papillae; type 3 and type 4 secretory cells in hillocks), and covering cells. They represent two types of adhesive systems: in the former, the two types of secretory cells would be adhesive; in the latter, one type of secretory cell would be adhesive and the other de-adhesive. Papillae are the site of entrapment of food particles while hillocks -together with the secretory cells of the ambulacral groove- are involved in embedding the particles in an adhesive material before they are carried along to the mouth.
