NERVOUS-SYSTEM OF THE LARVA OF THE ASCIDIAN MOLGULA-CITRINA (ALDER AND HANCOCK, 1848)

Features of the nervous system, especially those of the peripheral ner vous system, are described in the larva of Molgula citrina. In the per ipheral nervous system, antibodies raised against acetylated alpha-tub ulins mark a pair of rostral nerves arising from 8 to 10 sensory cells in the trunk epithelium, and a pair of tail nerves. In the sensory ve sicle of the trunk, a pair of antennal cells is associated with the st atocyte, and a tuft of ca. 150 cilia is labelled inside the hypophysia l duct. A dorsal bundle of fibres forms a plexus over the surface of t he sensory vesicle which extends caudally over the visceral ganglion. The latter contains somata that were back-filled by Co2+-lysine throug h the cut tip of the tail. Antibodies directed against the transmitter candidates: peptides substance P, FMRFamide, somatostatin, neuropepti de Y, CGRP, VIP, and the amines: 5-HT, dopamine, noradrenaline and GAB A, all failed to demonstrate immunoreactivity anywhere in the nervous system. The trunk epithelium is ciliated uniformly but lacks papillae; this is remarkable given the presence of rostral nerves. The latter a re presumed to be sensory, and can be compared with those in larvacean s and the larva of amphioxus. Sensory cells in the tail nerve, if pres ent, lack cilia. The tail nerves are lateral in this species and presu med to be motor. (C) 1997 The Royal Swedish Academy of Sciences. Publi shed by Elsevier Science Ltd.