Family Pneumodermatidae Pelseneer, 1887
Pneumodermatidae is composed of six genera (Pneumoderma, Pneumodermopsis, Schizobrachium, Abranchaea, Platybranchium, Spongiobranchaea).
Pneumodermatidae have no shell (a small cup shaped shell is produced only in the embryonic stage and is lost during the first days of development). A mantle and mantle organs are absent in all Gymnosomata. This family is characterised by sucker arms, either two lateral arms or a median and two lateral arms. The buccal mass contains a well developed radula and a pair of hook sacs filled with numerous hooks. Gills are usually found at the posterior body pole and in the middle of the right lateral side. In juvenile specimens, bands of cilia are found where gills will develop and around the hood, covering the proboscis and buccal organs. The visceral mass fills the whole or part of the body and provides it with colour when chromatophores are absent in the skin. The wings are found beneath the mouth at both sides of the body with the lateral and posterior footlobes in between. The penis, absent during the female stage, is evaginable and in some species provided with an extra sucker. In species where this sucker is not found a special tubercle is found on the base of the posterior footlobe. A seminal groove runs from the sexual opening to the penis. The anus and renal aperture opens close to the osphradium, anteriorly at the right of the ventral side. Chromatophores are usually found in the skin.
[6 genera]