- Used as a particular epithet; without gills.
- An obsolete order of annelids, so called considering that the types creating it do not have special organs of respiration.
- some of a number of gill-less creatures excluding Abranchia.
- several annelids, so-called considering that the types creating it don't have any unique organs of respiration.
- A term often made use of as similar to Abranchia.