Giant tubeworms

Figure 1. The giant tubeworm Riftia pachyptila. (A) Dense aggregation at a hydrothermal vent of the East Pacific Rise. (B) Life cycle with aposymbiotic phase from fertilized egg to settled larva (blue), and symbiotic phase from larva in metamorphosis to adult (red). Infection of Endoriftia (red) from a free-living microbial community occurs in the larva. (C) Relationships of siboglinids outlining a hypothetical scenario of evolution of symbiosis in the trophosome originating from several tissues in the last common ancestor with a thiotrophic symbiont (pink) to the gut in frenulates, the visceral mesoderm in vestimentiferans and Sclerolinum, and the somatic mesoderm with a heterotrophic symbiont (yellow) in Osedax. Giant tubeworms