This worm was first described in 1828 by the British zoologist John Edward Gray as Themiste hennahi, the type specimen having been collected by the Rev.

The introvert (the retractable anterior part of the worm) is tipped by a crown-like structure of six branching tentacles which surround the mouth.

It burrows into sandy, gravelly, silty and muddy substrates in the intertidal zone, including eelgrass beds, and conceals itself under loose rocks.

[4] This worm often lives in a burrow or other low-oxygen environment, extending its introvert into the water column to feed.

Research has shown that the tentacular crown is the main respiratory surface, leading to this worm being described as a "tentacle breather".