trochophore

A trochophore is a free-swimming larval stage found in several invertebrate groups, most notably many molluscs and annelids, and also present in some related phyla. The name comes from Greek words meaning wheel-bearing, referring to the characteristic circular arrangement of cilia on many trochophore larvae.

Morphology of the trochophore typically includes a well-developed apical tuft of cilia at the anterior end and one or more bands of cilia used for movement and feeding. The preoral ciliated band, or prototroch, encircles the body just in front of the mouth, often giving the larva a wheel-like appearance. In some species a postoral band, the telotroch, runs along the posterior surface. The gut forms during development and the mouth typically develops near the front, with subsequent differentiation of the larval organs as it grows.

Development and ecology: Trochophores arise as part of the life cycle of many marine molluscs and annelids, among others, from embryos produced by spiral cleavage. They are typically planktonic and may be lecithotrophic (relying on yolk) or planktotrophic (feeding on plankton) during their larval phase. The larva is usually short-lived and metamorphoses into the juvenile adult form when environmental conditions or developmental cues trigger settlement.

Evolutionary significance: The trochophore is often regarded as a characteristic ancestral larval stage of the lophotrochozoans, illustrating a shared developmental plan across several phyla. Many lineages have modified, simplified, or lost the trochophore in favor of direct development or alternative larval forms, such as veligers in molluscs.