The Pericardial Sacs ofOcypodein Relation to the Conservation of Water, Molting, and Behavior

Abstract

The surface area of pericardial sacs of the semiterrestrial crab, Ocypode cordimana , is greater than that of pericardial sacs of the intertidal crabs, Ocypode macrocera and Ocypode platytarsis . Responses of the pericardial sacs with relation to conservation of water and molting vary with the species. In the semiterrestrial crab, Ocypode cordimana , the pericardial sacs store water during proecdysis which is used to stretch the new cuticle after ecdysis. In contrast, the pericardial sacs of the intertidal crabs, Ocypode macrocera and Ocypode platytarsis , do not store water during proecdysis. But the sacs of these crabs swell for a brief period during ecdysis, apparently to accommodate excess fluid entering the body while the legs are being withdrawn from the old exoskeleton. Although the significance remains unknown, deposits of uric acid are found in the pericardial sacs of Ocypode cordimana but not in the pericardial sacs of Ocypode macrocera and Ocypode platytarsis . Exposure of specimens of Ocypode cordimana to dry sand reduces the swelling of pericardial sacs, while proecdysial growth of the limbs remains unaffected. The pericardial sacs of Ocypode cordimana swell at a rapid rate if the crabs are maintained in darkness rather than in light. Implications of the present findings are discussed with relation to the habitat of the crabs.