CENTRAL NERVOUS SYSTEM OF HUTCHINSONIELLA MACRACANTHA (CEPHALOCARIDA)

The central nervous system of the cephalocarid Hutchinsoniella macracantha is well developed, although missing several structures which are characteristic of the general crustacean plan. There are no signs of eyes either in the adult or in the larva. The organ of Bellonci, central body, protocerebral bridge, and paracentral lobes are absent. The mushroom bodies occur in the central nervous system in a form different from that found in malacostracan crustaceans and are unexpectedly well developed. They are connected to the olfactory lobes, which in this species are displaced ventrally into the clypeus (anterior part of the so-called labrum), extremely large, and of hitherto unseen construction. The central nervous system of Hutchinsoniella does not conform to a paradigm of overall primitiveness and must have evolved separately in the cephalocarid line for a long period.