There is no armed protrusible pharynx, such as exists in some other Chaetopods.
This may be associated with mud-eating habits; but it is not wholly certain that this is the case; for in Chaetogaster and Agriodrilus, which are predaceous worms, there is no protrusible pharynx, though in the latter the oesophagus is thickened through its extent with muscular fibres.
The male ducts are either one pair or two pairs, which open by a common and complicated efferent terminal apparatus furnished with a protrusible penis.
Each testis communicates by means of an efferent duct with a common collecting duct of its side of the body, which opens on to the exterior by means of a protrusible penis, and to which is sometimes appended a seminal vesicle.
- A protrusible proboscis exists, but there are no jaws.