At first it is short but it is widened and extended as the worm grows, sometimes reaching a length of more than 7 centimetres (2.8 in) [2] and a diameter of 4 millimetres (0.16 in).

The worm is largely hidden within the tube but it has a yellow or golden-coloured operculum and a number of fine tentacles which it extends in order to feed.

Each larva has a ciliated band with two bundles of long, barbed setae (bristles), one on each side of its body.

Another band of short cilia at the posterior end of the larva enable it to swim, and when it is doing this, the setae are held alongside the body.

[4] In Puget Sound, Washington, aggregations of up to 3,500 tubes of Neosabellaria cementarium per square metre at depths of between 15 and 40 metres (49 and 131 ft) were found to provide a habitat to a diverse range of other organisms not found in adjacent areas.