No abstract

Nitrogen excreted into the urine (<1 mM) has generally been considered a negligible component of total nitrogen output of crustaceans. But concentrations of ammonia >100 mM were found in the urine of laboratory-held Ocypode quadrata, suggesting that this notion might not be applicable to all crustaceans. To address this issue, hemolymph and urine were removed from freshly captured O. quadrata and analyzed for nitrogenous catabolites and major ions. Hemolymph composition was similar to that of other crustaceans, but the urine was acidic ({Xbar} pH = 5.50) and contained ammonia, often at >100 mM. Other nitrogenous catabolites in the urine (urea, amino acids, and uric acid) were much less concentrated: totaling <12 mM on average. The ionic composition of the urine was similar to that of other crustaceans, with the exception that Na was much less concentrated than Cl-. Total osmolality of hemolymph and urine was similar. The Na+/K+ ATPase activity was greater in the antennal glands than in the posterior gills of O. quadrata, suggesting that this enzyme is important for ammonia concentration and Na resorption. This pattern of enzyme activity was not present in two terrestrial brachyurans whose urine contains little ammonia. The evolutionary significance of high ammonia concentrations in the urine of ghost crabs is unclear.

No abstract

Abstract. During the summer of 1989, we examined mechanisms of egg hatching in three species of brachyurans that occupy different habitats as adults near Beaufort, North Carolina, USA: Neopanope sayi (Smith) (subtidal), Uca pugilator (Bosc) (intertidal) and Sesarma cinereum (Bosc) (supratidal). Results of casein assays indicated that embryos of all species release proteolytic enzymes near the time of egg hatching. Species differences in specific enzyme activity were suggested, with increased activity in the more terrestrial crabs. Embryos of AT. sayi released enzymes several hours before larval release by the female, while U. pugilator and S. cinereurn released enzymes closer to the time of larval release; enzyme release coincided roughly with time of egg-membrane breakage in all species. Direct observations of hatching showed a sequence of outer-membrane breakage apparently followed by inner-membrane breakage and emergence of the larva. Egg volumes increased most during early and/or mid-stages of development, with a marked slowing of the increase during the several days before hatching. Thus, a gradual osmotically-driven increase in water content may also be involved in egg hatching.