Riftia

Riftia is a genus of deep-sea tube worms in the family Siboglinidae, best known from hydrothermal vent environments. The most famous species, Riftia pachyptila, was described from vent fields along the East Pacific Rise and has since become a model organism for vent ecosystems. Members of the genus are typically found attached to vent substrates, sometimes forming dense aggregations around vent openings.

Anatomy and physiology: Riftia lack a mouth, gut, and anus. Their body is divided into a large anterior vestimentum and a posterior opisthosome, surrounded by a protective tube secreted by the worm. A prominent red plume protrudes from the vestimentum and contains hemoglobin capable of binding oxygen and hydrogen sulfide, delivering both to endosymbiotic bacteria housed in the trophosome. These chemoautotrophic bacteria oxidize sulfide to fix carbon, providing nutrients to the worm. The tube and trophosome together support a life strategy that does not rely on external feeding in the usual sense.

Ecology and life history: Riftia rely on their internal symbionts for nutrition, enabling them to inhabit oxygen-poor, sulfide-rich vent habitats. They can reach lengths of up to about two meters. Reproduction is believed to involve the release of free-swimming larvae that disperse with ocean currents before settling to form new individuals or populations.

Discovery and significance: Riftia pachyptila was described in 1977 from hydrothermal-vent fields in the Pacific. The genus represents a key example of chemosynthetic symbiosis and has helped redefine understanding of life in extreme deep-sea environments.