Family Hydromylidae Pruvot-Fol, 1942
The Hydromylidae consists of one genus only.
The families Hydromylidae and Laginiopsidae are two bizarre families both represented by only one species and the latter by only one specimen and they differ from all other Gymnosomata. Laginiopsis is characterised by its proboscis, terminated by three large, rounded lobes; in between these lobes the mouth is found dorsally (anterior to ventral is normal for Gymnosomata). Jaw and radula are absent. There are no gills, but the wings and footlobes are similar to other Gymnosomata. Hydromylidae are even stranger, the wings are spur-like with large anteriorly projecting lateral footlobes in between. These lateral lobes are connected directly with the sometimes bilobed, anterior tentacles. The visceral mass, to which the head is fixed, is attached by two pairs of muscles to the outer integument which itself is not in contact with the visceral mass. The outer integument is a stiff capsule in which the animal can completely retract. Hooks are absent, radula and jaw are reduced. The stiff integument is by some authors compared to the shell by some authors, however, it is an unique structure.
[1 genus]