Pogonophora

Pogonophora (beard worms) A phylum comprising deep-sea worms, first encountered in early Cambrian rocks but discovered only in the 20th century. Beard worms bear a superficial resemblance to Polychaeta and it has recently been proposed that they are actually very highly specialized polychaetes. They live at great depths inside chitinous tubes they secrete for themselves in soft substrates, often in the vicinity of hydrothermal vents. The body is coelomate, partly segmented, has ‘bristles’ (chaetae), and is divided into three parts, the anterior crowned with tentacles. 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. The animals are believed to obtain nourishment through a chemosymbiotic association (see CHEMOSYMBIOSIS) with bacteria. There are two groups, one found near vents and cold seeps, the other occurring widely in all oceans.