The distribution and organization of CAP sensillae in decapod crustacea

The organization of peg‐like sensillae composing CAP organs is described for a number of representative decapod crustacea. In Natantian forms the sensillae are aligned in linear fashion on the distal side of the appropriate joints. One example, Pasiphaea, possesses a cluster of hair sensillae instead of pegs, possibly indicating the primitive origin of this organ system. In the Reptantia the Macrura have well‐developed groups of sensillae, arranged in broad fan‐shaped arrangements; the Anomura display rather varied plans of small sensillae, and in Porcellana only one group on maxilliped 3 are found. The Brachyura have no CAP organs. The significance of these findings, and their possible implication in the evolution of internal proprioceptors in the crustacea, is discussed.