Siboglinidae

Siboglinidae is a family of marine annelid worms within the phylum Annelida that includes several deep-sea tube-dwelling lineages. Historically known as Pogonophora, the Siboglinidae are now recognized as part of the polychaete annelids and encompass diverse groups such as vestimentiferans, frenulates, and the bone-eating Osedax. Members occur primarily in deep ocean habitats, including hydrothermal vents, cold seeps, whale falls, and other organic-rich substrates.

Anatomy and feeding biology are distinctive. Adult siboglinids typically lack a conventional digestive tract. Their bodies are divided into regions, with a specialized tissue rich in symbiotic bacteria called a trophosome. These endosymbionts are chemoautotrophs that derive energy from reduced compounds (such as sulfide or methane) and, in turn, supply nutrients to the worm. Most species live inside protective tubes secreted by the worm itself, and some lineages show pronounced body regions such as a vestimentum that anchors the worm and a posterior region that houses the trophosome.

Ecology and distribution are centered on chemosynthetically driven ecosystems. By hosting symbiotic bacteria, siboglinids contribute to primary production in environments where light-driven photosynthesis is absent. They are key components of vent and seep communities and can influence habitat structure through tube-building activity and, in the case of Osedax, specialization on bone substrates.

Reproduction and life cycles vary among lineages, but generally involve sexual reproduction with larval stages that enable dispersal in the ocean. This group has played a crucial role in understanding deep-sea biology, symbiosis, and the evolutionary history of annelids.