A non-feeding pilidium with apparent prototroch and telotroch.

The nemertean pilidium larva is a long-lived planktotrophic form which is challenging to homologize to other invertebrate larval forms. Here we report a reduced, lecithotrophic pilidium which superficially resembles a trochophore. We document the pilidium-like catastrophic metamorphosis of this larva, including devouring of the larval body. Sequences of COI and 16S rRNA show that this larva belongs to an undescribed lineiform species. This novel larval form highlights the long-standing question, is the trochophore a conserved larval ground-plan or a functional design arrived at by convergence?