Behind the mouth, and close to the nephridium, which is raised on a protuberance, are two chetae (bristles), the bases of which are buried in the muscle.

The colour of the trunk is a dark, greyish-green, the proboscis is rather paler, and the edges of the forked tip are whitish.

The ovarian tissue is situated alongside the ventral blood vessel and the nephridium consists of several interconnecting sacs.

The males live inside one of the sacs of the female's nephridium, where the eggs are also stored, and obtains its nutrition from the fluid in which it is immersed.

[3] This worm immerses itself in the sediment or hides its trunk under a rock, extending its proboscis with its two-pronged tip flattened over the substrate.