Vestimentiferans

Vestimentiferans are a lineage of large, tube-dwelling annelid worms in the family Siboglinidae, within the clade Siboglinida. They are most famous for inhabiting deep-sea reducing environments such as hydrothermal vents and cold seeps, where they form dense colonies around and within hard substrates. A defining feature is the complete absence of a conventional digestive tract; vestimentiferans rely on endosymbiotic bacteria housed in a specialized organ called the trophosome to meet their nutritional needs.

Anatomy and feeding ecology: The body is divided into a anterior vestimentum that projects outside the tube and bears a reactive plume, and a longer opisthosoma that extends within the tube. The plume consists of feathery radioles used for gas exchange and may appear bright red due to hemoglobin-rich blood that transports both oxygen and sulfide to the symbionts. The worm lives in a chitinous or proteinaceous tube secreted by its epidermis, anchoring it to the seabed. Inside the trophosome, intracellular chemoautotrophic bacteria oxidize sulfide (and in some species methane) to fix carbon, supplying organic nutrients to the host. The worm, in turn, delivers vent fluids rich in reduced compounds to the bacteria via its circulatory system.

Habitat and life history: Vestimentiferans are restricted to deep-sea reducing environments worldwide, including mid-ocean ridges, back-arc basins, and seep sites. Reproduction is sexual, with adults releasing gametes into the water column; larvae are free-swimming and eventually settle to form new colonies.

Notable genera and species include Riftia (Riftia pachyptila, the giant tube worm), Lamellibrachia, Escarpia, and Tevnia. Vestimentiferans are key examples of chemoautotrophic symbiosis in the deep sea and have driven major advances in our understanding of vent ecosystems.