see text Bonelliidae is a family of marine worms (Subclass Echiura, of the class Polychaeta, in the phylum Annelida) noted for being sexually dimorphic, with males being tiny in comparison with the females.

The ventral side of the proboscis has a ciliated channel along which food particles and mucus are moved towards the mouth.

The anus is at the posterior end of the body and two anal vesicles with ciliated funnels open into the cloaca.

The anal vesicles of the females are sac-like and bear the ciliated funnels on tubules, which branch in most genera.

[3] Males are quite different in appearance; the minute, ciliated body consists of little except a gonad, a seminal vesicle and two protonephridia.