Function of the pericardial sacs during the molt cycle in the land crab Gecarcinus lateralis

Abstract

AbstractThe hypothesis that the pericardial sacs of the land crab Gecarcinus lateralis directly take up and store proecdysial water has been investigated. At all stages of the molt cycle, the convoluted surface of the pericardial sacs apposed to the carapace forms a system of channels for capillary transfer of ground water to the gills. When exposed to an osmotic gradient in vitro, isolated intact pericardial sacs from normal or dehydrated intermolt, premolt, and postmolt crabs show no hydrosmotic response. Permeability to 3H2O (THO), expressed as hourly water exchange, is low for sacs under such conditions. If the separated old cuticle has been removed from sacs of late premolt crabs, up to 40 μl of water are gained in the first 15 minutes of exposure to an osmotic gradient, and the hourly exchange rate of THO is increased 30‐fold. These findings indicate that the pericardial sacs may allow osmotic entry of proecdysial water as detachment of the old cuticle takes place. From analyses of osmotic pressure, cations, and 14C‐insulin space of both hemolymph and pericardial sac fluid, it appears that the pericardial sacs do not store water per se but expand to accommodate an increasing hemolymph volume as proecdysial water enters the whole animal. Although water uptake occurs over a longer period in G. lateralis, the pattern of preparation for ecdysis is similar to that of all other brachyurans.