SALT AND WATER ANATOMY, CONSTANCY AND REGULATION IN RELATED CRABS FROM MARINE AND TERRESTRIAL HABITATS

Abstract

Fresh weights and blood specific gravities of land crabs (Gecarcinus lateralis), ghost crabs (Ocypode albicans) and mangrove crabs (Goniopsis cruentatus) are not significantly altered by exposure to salinities ranging from 0 to 720 mM C1/1. The fractions of total water content available for dilution of thiocyanate and inulin, 2/3 that of thiocyanate, are similar in the 3 species. Land crabs show adequate regulation of blood Cl concentration over a limited hypotonic range, ghost crabs over a hypo-and hypertonic range with the production of a urine which wastes Cl in hypotonic fluids, and mangrove crabs a more closely held regulation over this wider range with urine Cl levels more nearly approaching environmental concentrations. There is an apparent correlation between the inulin filtration rates and the availability of water in the habitats of the 3 species. Antennal gland filtration and reabsorption rates are adequate to account for electrolyte loss in mangrove crabs in distilled water, but in all other fluids, and in the other 2 species in all fluids, a route other than the antennal gland is indicated. Data presented suggest the similarity of mechanisms and thresholds involved in antennal gland function and the persistence of electrolyte loss, even in situations where ions must be rapidly absorbed to maintain constancy. The effectiveness of the regulation in mangrove crabs and the maintenance of a concentration gradient in land crabs can be related to the successful adaptation of these 2 species to totally different habitats.