Figure 1

Schemes of organization of the nerve system in juvenile (A, B, D) and competent larvae (C) of Phoronopsis harmeri . Nerve elements are shown by different colors. Although the homology between larval and definitive nerve elements is still uncertain, some nerve elements, which juvenile certainly inherits from larva, are indicated by the same colors in juvenile and in larva. (A) The scheme of cross section of tentacle. (B) The scheme of innervation of definitive tentacles, which are viewed from the abfrontal side. (C) The nervous system of competent larva, which is ready for metamorphosis. All nerve elements, which were observed by TEM and immunocytochemical staining, are shown. Larva is viewed from the left; the apical is at the top, the ventral side is to the left. Picture was changed from Temereva and Tsitrin [8]; abbreviation are shown in the Table 1 and in Figure 4[8]. (D) Scheme of whole nervous system in 10-day-old juvenile. The lophophore is simplified; tentacles of the left side are removed. The oral side is to the left. The number of nerve fibers along the body reflects the density of the nerve plexus in different body parts. Abbreviations: a – anus; amp – ampulla; apt – anterior portion of the body; az – abfrontal zone; c – commissure; c2 – mesocoel; e – erythrocyte; fz – frontal zone; gf – giant fiber; gp – group of perikarya; itb – intertentacular branch; la – lateroabfrontal neurites; laz – lateroabfrontal zone; lf – laterofrontal neurites; lfz – laterofrontal zone; lz – lateral zone; m – mouth; ma – medioabfrontal neurites; mdn – most dorsal neurites, which probably correspond to second group of larval neurites (sg); mf – mediofrontal neurites; mnr – minor nerve ring; nc – nephridial channel; pt – posterior portion of the body; tn – tentacular (main) nerve ring; trn – trunk neurites; trp – trunk perikarya.