A physiological comparison of isopods in the transition from a marine to a terrestrial habitat : with notes on their morphology and behavior

This study is of five species of isopods common to the Dillon Beach area, each of which represents a different level in the transition toward land life. Cirolana harfordi was used as a completely marine form. Idothea (Pentidotea) wosnesenskii represents a step toward land life as it inhabits an area uncovered by most low tides. Ligia occidentalis is found in the splash zone, receiving spray from the action of the surf. This illustrates another, higher, level in the transition. Alloniscus perconvexus was the fourth species studied. It is commonly found burrowed in the sand in the area of the berm, which is the nearly level portion of the beach formed by high tidal wave action. Finally, the terrestrial form, Porcellio (Porcellion) scaber, was used to illustrate those isopods best adapted to land life. The physiological data presented in this paper includes salinity tolerances and humidity tolerances. Some information on acclimating one species to lowered salinities is also presented. The results of these experiments are used to illustrate the degrees of adaptation to land life shown by the isopods in different areas of the transition. A discussion of the adaptive morphology and behavioral characteristics is also related to the environmental situations in which each animal is found