Unlike the ciliate bands in
dipleurula larvae, however, the ONR develops later than the persistent CNS and centrally derived peripheral nerves.
So the main question is this: Are the trochophora and dipleurula larvae ancestral to protostomes and deuterostomes (or perhaps ambulacrarians), respectively, or have these larval types evolved convergently in several clades?
Filter-feeding with ciliary bands like those of trochophora and dipleurula larvae (see below) has not been observed.
This stem form gave rise to trochophore and
dipleurula ( = tor-naria) lineages, which each subsequently added a benthic stage to the life cycle.
The shared absence of serotonergic adoral ganglia in the auricularia and tornaria suggests that the ancestral
dipleurula larva also lacked this structure and may have employed other neurochemicals to modulate feeding behavior.