A preoral band of cilia, the prototroch
, encircles the larva and beats with an effective stroke from anterior to posterior.
The transformation of embryos to trochophore larvae occurred 17.5 h after fertilization, which included the formation of a pear-shaped body, a tuft of cilia in the episphere, and the ciliary ring above the mouth (prototroch
), which enabled the larvae to move (Fig.
with a band of fine cilia encircling the head, with the exception of the dorsal part (Fig.
The trochophoredeveloped into diamond-shaped covered by crown of cilia called prototroch
at anterior part.
The onset of development is intracapsular, a rapid formation of the locomotory prototroch
is no longer necessary, and the free-swimming phase is postponed to later developmental stages.
The velar edge had the ciliary bands typical of feeding veligers: prototroch
, metatroch, and food groove (Fig.
has abundant, elongated cilia and forms a crown towards the anterior end; granules of dark green vitellus can be observed at the posterior end of the larvae (Fig.
From the early trochophore stage (18 hpf), the ciliated prototroch
started to be transformed into the velum (22 hpf), the main larval swimming organ (Fig.
elegans are free-swimming planktotrophic animals with a ciliated prototroch
and metatroch and a collar (Fig.
A non-feeding pilidium with apparent prototroch
tenuis appeared to have only simple cilia in the prototrochal ciliary band; among planktotrophic larvae of annelids, simple cilia in the prototroch
were previously known only from members of Oweniidae.
Also during gastrulation, the blastopore and pretrochal region were ventrally displaced, situating the blastopore ventrally just below the developing prototroch