Stress detection at the autotomy plane in the decapod crustacea

Summary The preformed autotomy plane of most reptantian decapods circumnavigates the basi-ischiopodite of the pereiopods. Associated with discrete areas of soft or thin cuticle in the proximity of the breakage plane are two connective chordotonal organs. These organs are sensitive to cuticular stress and are referred to as Cuticular Stress Detectors (CSD).The CSD organs respond to pressure applied to the basi-ischiopodite and upon deformation of the discrete areas of soft cuticle onto which the connective tissue strands of the receptors insert. The CSDs exhibit a wide range of unit activity and both receptors have a similar population of unit types. Some units are active only on application or removal of a force applied to the soft cuticle but a large number of phaso-tonic and tonic units respond to a constant pressure applied to the soft cuticle. The majority of the units respond during application of the stimulus (ON units) but a small proportion of the units increase activity on removal of the stimulus (OFF units).Passively produced tension in the anterior levator (autotomiser) muscle and depressor muscle tendons of the C-B joint is a potent stimulus to both receptors.Both receptors respond to movement of the B-I joint of the Nephropsidean walking leg and to movement of the I-M joint in the pereiopods of other reptantian decapods where the basipodite and ischiopodite have fused. The degree of activity is not directly related to the joint position or direction of movement.During autotomy both receptors respond strongly, particularly CSD 1. CSD 2 also shows increased activity but as the receptor is located distal to the breakage plane the receptor nerve is severed when breakage occurs.After autotomy CSD 1 responds normally to deformation of the soft cuticle but manipulation of the breakage plane membrane or of the regenerating limb bud produces low levels of activity even though the stimulus is gross.The possible functional roles of the receptors are discussed.This work was supported in part by European Science Exchange Programme study visit grants awarded to F. Clarac and W. Wales.