siboglinids

Siboglinids are a group of marine annelid worms within the family Siboglinidae, a lineage that includes several forms formerly treated as Pogonophora or Vestimentifera. They are best known for living in deep-sea environments and relying on symbiotic bacteria for nutrition, rather than a typical digestive system.

Morphology and biology: Siboglinids include tube-dwelling vestimentiferans as well as bone-eating Osedax worms. Adults commonly lack a functional digestive tract and rely on endosymbiotic bacteria housed in a specialized tissue called the trophosome. Feeding and growth are supported by these chemosynthetic bacteria, which fix carbon using energy derived from sulfide or methane found in their environment. A plume or branchial region often provides gas exchange, and many species secrete protective tubes in which they live.

Ecology and symbiosis: The bacterial symbionts oxidize reduced compounds such as hydrogen sulfide or methane, supplying the host with organic nutrients. This arrangement enables siboglinids to thrive at hydrothermal vents, cold seeps, and other chemically rich habitats, including whale falls in the case of some species.

Habitat and distribution: Siboglinids are most abundant in deep-sea ecosystems. Vestimentiferans form large, colonial tube communities around vents and seeps, while Osedax colonize bones, notably whale carcasses, by attaching to and bore-holing into the substrate.

Reproduction and development: Reproductive strategies vary among siboglinids, but most species release eggs and sperm into the surrounding water, producing free-swimming larvae that disperse before settling in suitable habitats.

Significance: Siboglinids provide a key example of chemosynthetic symbiosis and play a notable role in deep-sea ecosystem functioning and nutrient cycling.