|Long, thin, bilaterally symmetrical, metamerically segmented worms|
|A body divided into three distinct regions; short forepart with 1 - 260 tentacles, long, slender trunk, short, segmented opisthosoma (holdfast).|
|A body wall of cuticle and epidermis, a central double band of cilia, and the opisthosoma may have chaetae|
|Closed blood system with heart|
|Separate sexes, fertilisation uncertain, but thought to be external|
|They do not have a mouth, anus, or gut at any stage of their life-cycle.|
Pgonophora were first described in 1900, but it was not until 60 years later that whole specimens were obtained. The early descriptions did not include the opisthosoma (see above). To date about 100 species have been described, all coming from depths of 20 - 4000 m.
The worms range in length from 5 - 300 cm, and all are less than 3 cm in diameter. They live in a self-secreted chitinous tube the length of their body, buried vertically in fine sediments.
Their body is divided into 4 regions:-
They appear to have a mutualistic association with chemoautotrophic bacteria which live in their body, and nutrients are absorbed through their hollow, anterior tentacles. About half-way down their trunk they have two rings of chaetae which anchor to the tube wall.
They may share a common ancestor in the Annelida, but there is no fossil record.