Osmoregulation and FMRFamide-related peptides in the salt marsh snail Melampus bidentatus (Say) (Mollusca: Pulmonata)

The pulmonate snail Melampus bidentatus occupies the high intertidal zone of salt marshes in a nearly terrestrial environment. The hemolymph osmolarity of the snails collected in the field paralleled that of the adjacent water and was affected by the tides and precipitation. The snails initially gained or lost weight when submerged in hypo- or hyperosmotic media, respectively, but returned to their original weight after 24 h. The content of their immunoreactive (IR)-FMRFamide-Related Peptides (FaRPs) was measured in various tissues by radioimmunoassay, and IR-FaRPs were found in every tissue analyzed. The subesophageal part of the central nervous system (CNS) contained more IR-FaRPs than the supraesophageal part, and the kidney and the tissues of the reproductive tract contained more than other peripheral tissues. The levels of IR-FaRPs in the CNS, kidney, and hemolymph were higher in snails that were immersed in higher concentrations of seawater. Many IR neurons are present in all ganglia of the CNS except the pleural ganglia, and IR neurites are extensively distributed within the CNS and its connective tissue sheath. The visceral nerve from the visceral ganglion is immunoreactive and could be seen to innervate the kidney, which contains IR-varicosities. An osmoregulatory role for the FaRPs is suggested.