THE PERISTOMIAL MEMBRANE OF REGULAR SEA-URCHINS - FUNCTIONAL-MORPHOLOGY OF THE EPIDERMIS AND CELOMIC LINING IN PARACENTROTUS-LIVIDUS (LAMARCK)

The functional organization of both the epidermis and the coelomic lin ing of the peristomial membrane in the regular sea-urchin Paracentrotu s lividus is described and correlated with the extreme deformability o f the peristomial membrane and with the ''miltability'' of its related dermis. The epidermis consists of a monolayer of columnar supporting cells mixed With ciliated sensory cells, the wide interspaces between these epithelial cells being oc cupied apically by a variety of cell t ypes and basally by a conspicuous basiepithelial nerve plexus. The coe lomic lining is a peripharyngeal coelomic epithelium consisting of api cal monociliated peritoneocytes and subapical myocytes, and has an ass ociated basiepithelial nerve plexus. Although the basic morphology of these epithelia is similar to that of corresponding tissues in other e chinoderms, they both have significant structural adaptations and disp lay the histological pattern of typical transitional epithelia, which enables them to match the wide range of deformations shown by the peri stomial membrane in vivo. Histofluorescence techniques were employed t o explore the innervation of the outer epidermis and the inner coelomi c lining.