; phylum Aschelminthes)
A small class or phylum of pseudocoelomate, unsegmented worms, the vast majority of which are marine. Their narrow, hair-like bodies have a thick cuticle. All lack a true excretory system. The young are parasitic, and mature individuals are free-living in fresh water. They are first recorded from the Eocene.
Subjects: Zoology and Animal Sciences — Ecology and Conservation.