Scanning electron microscopic observation of the statocyst in the crayfish Procambarus clarkii Girard

The statocyst in the crayfish Procambarus clarkii was investigated using scanning electron microscopy. The statocyst contains static hairs arranged in four group, i.e. lateral, medial, proximal, and distal. All the hairs are the same in basic structure. They differ in length and diameter and in their position with respect to the other hairs in the group and to the statolith. In terms of morphological polarization, the hairs in the lateral and medial groups are polarized toward the center of the crescent, while the hairs in the proximal group are polarized away from the center of the crescent. In the distal group, most hairs are polarized toward the center of the crescent, while some hairs are at random. This morphological polarization may be consistent with that of functional polarization. The statolith overlays the lateral and medial hair groups. The hairs in the distal group do not touch the statolith, whereas the hairs in the proximal group make contact with it from the side. It has been therefore indicated that the lateral, medial and proximal groups could detect gravity and linear acceleration like macular end organs and distal group could detect angular acceleration like semicircular canal in mammals.