The structure and growth of the statocyst in the Australian crayfish Cherax destructor

The morphology of the statocyst of the Australian crayfish Cherax destructo r was examined using scanning electron microscopy. It resembles in general structure, size, and position the statocysts of crayfish described previous ly, and the size and distribution of the fields of setae on the floor of th e capsule are similar but not the same. Over the size range examined, the r elationship between the carapace length, the length of the basal antennular segment, the diameter of the statocyst capsule, and the total number of se tae are all linear. The number and position of setae on the floor of the st atocyst capsule were mapped for animals in two size classes (small, ca. 20 mm; large, ca. 50 mm) to test for changes in their arrangement during growt h. The change in the ratio of setal number to statocyst size between the tw o size classes was about three times greater for the anterior setal field t han for the other fields. We propose that differential development of the s etal fields may be related to changes in the force-monitoring requirements of the animals as they increase in size, but this remains to be experimenta lly tested.