Family Pterotracheidae Gray, 1840
Pterotracheidae comprises two genera: Pterotrachaea and Firoloida. They have completely lost their shell and the visceral nucleus "determines" its own shape, which differs in the different species. The anatomy is identical to that of the Carinariidae. The body is, however, more elongated and the visceral nucleus is placed more posteriorly towards the end of the trunk.
[2 genera]