Ciliation in P. lamarckii. Visualized by immunohistochemistry with anti-acetylated tubulin. Scale bars = 50 μm. A. Early gastrula, dorsal view, apical is to the top. The cilia of the prototroch (pt) are present and function at a very early stage. The ring is initially open on the dorsal side (*). B. Gastrula, apical view. Shortly after prototroch formation the apical tuft (at) is formed. The prototroch is still open dorsally. C. Early trochophore, ventral view, apical is to the top. The mouth (m) has now reached its final location. D. Early trochophore, posterior view. The adoral ciliary zone (ad) has begun to form in a ring lateral to the mouth. Posterior to this the metatroch (mt) begins to form. Ciliation in the oesophagus and stomach (st) is evident at this stage. E. Complete trochophore, left lateral view, apical is to the top. At this stage ciliary bands including the longitudinal neurotroch (nt) are complete. A tuft of cilia emerges from the anus (a). F. Complete trochophore, ventral view, apical is to the top. Paired protonephridia (pn) run anteriorly from the anus. G. Complete trochophore, posterior view. Extensive ciliation in the oesophagus and stomach is visible. H. Metatrochophore, left lateral view, apical is to the top. Ciliation is similar to previous larval stages, but protonephridia are not visible. The neurotroch no longer reaches the mouth. I. Juvenile, ventral view, anterior to the left. The juvenile shows reduced ciliation, with the branchial crown (bc), intestine (in) and anal tuft (a) the only features visible. Remnants of the mucous tube (mu) are apparent.