THE NERVOUS-SYSTEM OF THE TROCHOPHORE OF HARMOTHOE-IMBRICATA (POLYCHAETA)

The development of the neural structures in the larvae of Harmothoe im bricata was studied in details using neurohistological techniques. Sig nificant differences in the architectonics of nervous system between l arvae and adults support the hypothesis (Bubko, Minichev, 1978) of mul ti-stage ontogenetic and phylogenetic formation of nervous apparatus i n trochophoral animals. Circular and longitudinal neural structures co mparable to the elements of ortogon in turbellarians are absent in tro chophores. The data prisented in this paper and in our earlier publica tions lead to the conclusion about the independent origin of nervous s ystem from primary diffuse neural plexus in different phylogenetic bra nches.