A note on the obligate symbiotic association between crab Zebrida adamsii White, 1847 (Decapoda: Pilumnidae) and Flower Urchin Toxopneustes pileolus (Lamarck, 1816) (Camarodonta: Toxopneustidae) from the Gulf of Mannar, India

On some commensal anomuran and brachyuran crabs (Crustacea: Decapoda) off Visakhapatnam, Northwestern Bay of Bengal

Commensal anomuran and brachyuran crabs were collected from extensive exploratory surveys on rocky areas where soft corals, sea anemones and sponges are found off the Visakhapatnam coast. The present study includes nine species of commensal decapod crustaceans, comprising four porcellanid crabs (Petrolisthes lamarckii (Leach, 1820), Porcellanella triloba White, 1852, Polyonyx hendersoni Southwell, 1909 and Pisidia gordoni (Johnson, 1970)), one squat lobster (Allogalathea elegans (Adams, 1847) and four brachyuran crabs (Dorippoides facchino (Herbst, 1785), Quadrella coronata Dana, 1852, Quadrella maculosa Alcock, 1898 and Sphenomerides trapezioides (Wood-Mason & Alcock, 1891). Allogalathea elegans, Polyonyx hendersoni, Pisidia gordoni, Quadrella coronata and Quadrella maculosa are new records from off Visakhapatnam. The porcellanid crabs are associated with the sea pen Pteroeides esperi, desmosponges and black soft corals Antipathes sp. whereas the squat lobster was associated with the soft coral Dendronephthya sp. The brachyuran crabs were observed in association with Antipathes sp. Here, we provide details on the morphology, distribution, habitat and commensalism of decapod crustaceans studied.

Dumbbell-Shaped Ossicles Discovered in Pedicellaria of Flower Sea Urchins

Sea urchins have a globiferous pedicellaria that stands from a test with a stalk on which lies a head made of three movable jaws with venom-injecting teeth. The globiferous pedicellariae of the flower sea urchin Toxopneustes pileolus, one of the most developed among sea urchins, are unique in that the jaws are provided with a jaw membrane that gives the pedicellaria an appearance of a flower when the jaws are open. We observed this membrane in an ionic liquid that does not require processes, such as fixation, dehydration, or coating with conductive materials, for observation with a scanning electron microscope. Using this technique, we discovered dumbbell-shaped ossicles, which consist of two spheres of similar size connected by a cylinder. The diameter of the sphere is 4-8 µm, and the total length of the ossicle is 10-20 µm. The jaw membrane is trimmed with an edge zone. The ossicles were found sparsely in the connective tissue of general part of the membrane, but in the edge zone their density was so high that neighboring ossicles were in close contact with each other. Some neighboring ossicles crossed their cylinders and some inserted one of their spheres to snugly fit in the gap between the spheres of neighboring ossicles. Their structural role is very likely in strengthening the jaw membrane, probably serving as fillers in the general part of the membrane; in the edge zone the interlocking of adjacent ossicles forms a loose network providing a firm frame for the head of the globiferous pedicellaria. When opened, the stiff frame prevents the membrane from sagging. When clasped, it works as a closed door, firmly keeping prey trapped.