Hydrostatic pressure changes in the abdomen of the hermit crabPagurus pollicarus during movement

Abstract

1. The hermit crabPagurus pollicarus maintains an internal pressure of from 4 to 10 g/cm2 in its abdomen; this increases by two to 3 g/cm2 during lift of the shell and walking. 2. Characteristic pressure changes during flexion and extension are described; in addition, the response of pressure and motoneuron firing frequency is correlated during these movements. 3. The motoneurons of the ventral superficial muscles reponds to pressure changes in the abdomen with a long latency high threshold rapidly adapting response; it is concluded that this is due to stimulation of touch receptors in the skin. 4. There is no relationship between abdominal load and internal pressure. In addition, the slopes and intercepts of load-abdominal extension curves were not significantly different from each other over a range of imposed internal pressures ranging from zero to 24 g/cm2. It is concluded that pressure does not generate lift in the absence of changes in muscle tension.