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The perimetamorphic period in Paracentrotus lividus lasts for 8-12 days. It starts from the acquisition of larval competence, includes the change in form (metamorphosis) and the endotrophic postlarval life, and stops with the appearance of the exotrophic juvenile. All major postlarval appendages already occur in competent larvae being either grouped into the echinoid rudiment (terminal plates, early spines and primary podia) or scattered within the larval integument (genital plates and sessile pedicellariae). Competent larvae show particular behaviour which brings them close to the substratum. The latter is tested by primary podia protruding through the vestibular aperture of the larva. Primary podia are sensory-secretory appendages that are deprived ampullae. They are able to adhere to the substratum in order to allow evagination of the echinoid rudiment (i.e. metamorphosis) and substatum adhesion of the postlarva. Particular spines are borne by the postlarva; these are multifid non-mobile appendages forming a kind of protective armour. Like those of the larva, all characteristic structures of the postlarva (primary podia, multified spines and sessile pedicellariae) are transitory and regress either at the end of postlarval life (primary podia) or during early juvenile life (multifid spines and sessile pedicellariae). Other appendages that develop during postlarval life (i.e. podia with ampulla, point-tipped spines and sphaeridiae) are similar to those borne by the adults and become functional when the individual enters its juvenile life. Thus, the perimetamorphic period appears to be a fully fledged period in the life-cycle of P. lividus, and presumably in the life-cycle of any other sea-urchin species.& b d y :

Individuals of several species of European regular echinoids are affected by a spectacular disease that causes conspicuous lesions on the echinoid body surface. It is a communicable non-specific disease that produces loss of appendages and necrosis of dermal and skeletal tissues. Preliminary investigations indicate that the pathogen is not an alga but could be a bacteria.

Individuals of Asterias rubens and Marthasterias glacialis use their podia in locomotion, anchorage, and feeding. Each podium consists of a stem with a disk at its tip. The stem allows the podium to lengthen, flex, and retract, and the disk allows the podium to adhere to the substratum. Adhesion of sea star podia seems to rely on the epidermal secretions of the disk and not on a mechanical sucker-like operation. The disk epidermis is made up of five cell types: nonciliated secretory cells (NCS cells) of two different types (NCS1 and NCS2), both containing granules that are at least partly mucopolysaccharidic in composition; ciliated secretory cells (CS cells) containing small granules of unknown content; nonsecretory ciliated cells (NCS cells); and support cells. The epidermal cells of the podial disk are presumably functioning as a duogland adhesive system that is involved in an adhesive/deadhesive process. The following model is presented. Adhesive secretions are produced by NCS1 and NCS2 cells (both of them have extruded some of their secretory granules in attached podia). These secretions constitute a layer of adhesive material between the podium and the substratum, this layer being the footprint left by the podium after it has become detached from the substratum. Deadhesion, on the other hand, would be due 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 plexus.

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Sea cucumbers possess a peculiar specialized defense system: the so-called Cuvierian tubules. The system is mobilized when the animal is mechanically stimulated, resulting in the discharge of a few white filaments, the tubules. Their great adhesivity, combined with their high tensile strength, allows Cuvierian tubules to entangle and immobilize potential predators. The cellular origin and composition of the Cuvierian tubule adhesive were investigated in the species Holothuria forskali by studying prints left on the substratum after mechanical detachment of the tubule. Polyclonal antibodies raised against tubule print material were used to locate the origin of tubule print constituents in the tubules. Extensive immunoreactivity was detected in the secretory granules of mesothelial granular cells, suggesting that their secretions make up the bulk of the adhesive material. Tubule print material consists of 60% proteins and 40% carbohydrates, a composition that is unique among the adhesive secretions of marine invertebrates. Although it is highly insoluble, a small fraction of this material can be extracted using denaturing buffers. Electrophoretic analysis of the extracts revealed that it contains about 10 proteins with apparent molecular masses ranging from 17 to 220 kDa and with closely related amino acid compositions, rich in acidic and in small side-chain amino acids. The adhesive from the Cuvierian tubules of H. forskali shares these characteristics with many marine bioadhesives and structural biomaterials.