Proprioceptive neurons of chordotonal organs in the crab, Cancer magister Dana (Decapoda, Brachyura)

The proprioceptive organs for the limbs of Cancer magister contain sensory endings embedded in an elastic strand to detect stretch and relaxation. The dynamic movement-sensitive neurons are of two types: those sensitive to relaxation and those sensitive to stretch of the chordotonal strand, which corresponds to flexion or extension of the joints. The cell bodies of sensory neurons associated with the planar chordotonal organs in the limbs are arranged within the elastic strand, whereas the organs that are more like a cord have the cell bodies of the dynamic movement-sensitive neurons outside the connective tissue strand. This study observed that the dynamic movement-sensitive neurons that are sensitive to relaxation have larger cell bodies than cells sensitive to stretch. No stretch-sensitive neurons were observed for the cord-shaped chordotonal organs. The static, position-sensitive neurons are distal in all the organs and have the smallest cell bodies. Mapping the functional distribution of the neurons has revealed that the various types of chordotonal organs have a similar pattern in soma location as in function. The purpose of this study is to describe this anatomical arrangement of the sensory neurons on a subset of chordotonal organs within the limb of the crab, Cancer magister so that species comparisons can be made, in the future.