Responses of the false limpet, Siphonaria pectinata (Gastropoda, Pulmonata) to osmotic stress

Abstract

Investigations were conducted on the littoral euryhaline molluso Siphonaria pectinata Linnaeus which inhabits the granite jetties near Galveston, Texas, Animals were subjected to a wide range of salinities, and the [delta-t-f] and sodium concentrations of the body fluids were measured under conditions of osmotic stress. Experiments were designed to investigate the possibility of some control mechanism being operative to explain this animalls tolerance to osmotic stress. Experimental evidenoe Is presented that fluctuations in the osmotic oonoentrations of the body fluids are largely due tp water movements. Evidence is further presented that fluotuations In the osmotio concentration,of the hemolymph may be effeotively reduced during stress for periods of up to 48 hours. This is done by physical exertion on the part of the animal, resulting in a tight binding of the mantle fringe and outer margin on the shell to the substrate. Such exertion effectively results in greatly reduced exposure of the soft parts of the animal to the stress environment. The end result is a resistance to swelling or shrinking in hypoosmotio and hyperosmotio situations. respectively. The results suggest that dessication in air and expo-sure to hypersmotic salinities of water yield similar end results in terms of deleterious effects on the body fluid concentration of the animal. A discussion is presented of the possible significance of the fact that the animals seem more tolerant to hyperosmotic than to hypoosmotic conditions. The significance of the animal's apparent mechanical osmoregulatory ability is also discussed.