Planktonic larva of various protostomous groups, i.e. Bivalvia, Gastropoda, Chitons, Euchiura, Polychaeta, and Scaphopoda. The larval body is top-shaped and equipped with a prototroch ciliated ring and an apical tuft; in some cases dotted with shell glands. In addition, there is often a perianal ciliary band, the telotroch, and a midventral band, the neurotroch. Trochophora larvae are transparent and can have a round, pear or diamond shape. The mouth is very distinct and a simple eye is sometimes visible.
Polychaete trochophora larvae show after some time extended hind areas, becoming segmented. This larva stage is called metatrochophora. Metatrochophore larvae have a body that is divided into a series of identical segments. On every segment, two-branched outgrowths are present with a long brush in each. The head is distinct.