THE INITIAL DEVELOPMENT OF GANGLIAR RUDIMENTS IN A POSTERIOR POSITION IN MYTILUS-GALLOPROVINCIALIS (MOLLUSCA, BIVALVIA)

Histochemical methods for cholinesterase activities were applied to embryos and early Larvae of the marine mussel Mytilus galloprovincialis Lamarck (Mollusca: Bivalvia: Mytilidae) and demonstrated that the cerebral ganglia, which are generally accepted as the first differentiating ganglia, appear after two bilaterally symmetrical nerve rudiments have developed in a posterior position prior to the trochophore stage. They are intimately associated with non-nervous superficial cells in two structures which have features of sensory organs.