Fig. 4. Larvae during the transition from auricularia larva to doliolaria larva. (A)
Serotonergic immunoreactivity of a late auricularia larva that has began the
transition into doliolaria larva. The ciliary band nerve tracts have shifted their
positions but remain continuous and none of the nerve tract parts are lost. The
nerve tracts in the anterior part of the larva show high serotonergic
immunoreactivity. The right anterior ventral ridge ciliary band has curved
toward the ventral midline (arrowhead), but the left tract has become straight
(arrow). (B) Serotonergic immunoreactivity in a larva during the transition from
auricularia to doliolaria larva. The ridges have been absorbed and the body size
has decreased. The posterior ventral ridge ciliary band nerve tracts have
elongated anteriorly (arrowheads), bringing the postoral ciliary band nerve tract
(arrow) with them. They are shifted to the left from the midline. (C) Serotonergic
immunoreactivity of a larva during the late stage of the transition. The anterior
ventral ridge ciliary band nerve tracts have become close to each other at the
ventral side, forming a circle (arrows). Cell bodies can be seen along the circle.
(D) 1F9 immunoreactivity of the same larva as in panel C. Signals can be seen
along the rearranging ciliary bands. The adult nervous system seen in Figs. 5 and
7 is not yet present. Scale bars: 100 μm.