DEVELOPMENT OF A PROPRIOCEPTIVE ORGAN ON THE WALKING LEGS OF THE ROCKLOBSTER JASUS-EDWARDSII (DECAPODA, PALINURIDAE) BY ORDERED ADDITION AND LOSS OF RECEPTOR ELEMENTS

Specimens of the puerulus stage of the rock lobster Jasus edwardsii we re collected as they settled from the plankton. They were raised in a closed marine aquarium system. The molt cases were collected with each ecdysis during growth. The development of the Cuticular Articulated P eg (CAP) organs on the walking legs of sequential molts from the same animals was studied using scanning electron microscopy. The number of CAP sensilla in the organ increased with each molt. The size of indivi dual CAP sensilla and the distance between them increased during growt h, with the result that the length of the organ also increased. Sensil la could be added or lost at each molt. The number of sensilla in each organ increased steadily, because the rate of addition was greater th an the rate of loss. Most new sensilla were added to the organ proxima lly and most losses occurred distally. New proximal sensilla appeared fully formed. As the animals grew, the distal sensilla became graduall y smaller until finally they were lost by a process of resorbtion. Thi s is the first example of development of a crustacean proprioceptor by ordered, sequential turnover of receptor elements. Since each sensill um is associated with a single neuron, the pattern of development has implications for the way in which the sensory nervous system associate d with the receptors develops.