The use of pleopods for shell water circulation and respiration by hermit crabs

Abstract

The use of the pleopods was investigated in two species of Diogenid hermit crabs, Dardanus arrosor and D. calidus. A transparent glass shell was used to observe the movements of the pleopods in hermit crabs. The movements consisted of periodic, irregular beating, which generated an irregular flow of the water within the shell.

A strong, regular beating movement was elicited when there was detritus or faeces in the shell, as was occupation of a new shell. Injection of water with a low oxygen concentration into the shell failed to induce any variation in the pleopod beating frequency (PBF), while the injection of water with a high CO₂ concentration induced a sudden PBF increase. When pH was varied and CO₂ concentration held at normal atmospheric level, there was a change in PBF. However, CO₂ variation alone, at constant pH, did not trigger any visible reaction. This suggests that there is a receptor for pH, which acts independently of the CO₂ concentration.

The function of males hermit crabs pleopods has always been obscure. However, at least in Dardanus, they are actively involved in water circulation within the shell for shell-cleaning and probably for ventilation.

Keywords:

• Respiration
• Pleopods
• Hermit crabs
• Anomura
• Decapoda
• Crustacea

Acknowledgements

Many thanks are due to John Davenport and Brian McMahon for their suggestions and critical reading of the manuscript, and to Patsy McLaughlin and Rafael Lemaitre for their suggestions and help with the literature. Our Florence University colleague Giorgio Papeschi devised the electrode for the gas measurements while Roberto Pepino, Piero Stoppioni, Andrea Dei and Dante Gatteschi taught us how to use the appropriate chemical buffers. The ARPAT crew, Alessandro Voliani and Roberto Silvestri, caught the hermit crabs for us, sometimes under very bad sea conditions. The glass shells are the ingenious product of Frits Akerboom, St. Andrews University.