Effects of overcrowding on floating behaviour in the mud whelk cominella glandiformis (Mollusca: Gastropoda)

Abstract

The mud whelk Cominella glandiformis (Reeve, 1874) was observed on a tidal flat “floating” upside down beneath the water surface. Study in the laboratory showed that, when C. glandiformis is “floating”, the foot is distended with blood to approximately twice its normal surface area. In the laboratory C. glandiformis “floated” only during daylight hours, and the incidence of “floating” increased markedly as specimens became more overcrowded. Possibly “floating” is a rapid dispersal mechanism in response to overcrowding; it may also assist respiration in the event of overcrowding producing anaerobic conditions. Its occurrence only during daylight hours suggests that a reaction to light may also be involved. © 1976 Taylor & Francis Group, LLC.