A phylum comprising deep-sea worms, first encountered in early Cambrian rocks but discovered only in the 20th century. Beard worms are coelomate (see coelom) and live at great depths inside chitinous tubes they secrete for themselves in soft substrates. The body is divided into three parts. The anterior is crowned with tentacles. Part of the body is segmented and the worms have chitinous bristles. Their most remarkable feature is the complete absence of a gut. This has led to difficulties with classification because it is impossible to distinguish the ventral and dorsal surfaces, and it has also led to several theories concerning the method of feeding. The animals obtain nourishment by absorbing nutrients released by symbiotic (see symbiosis) Bacteria. It has been proposed that the Pogonophora are actually very highly specialized bristleworms (Polychaeta, a class of Annelida).
Subjects: Earth Sciences and Geography — Ecology and Conservation.