The former Philinacea are (2011) part of the superfamily Philinoidea of Opisthobranch sea slugs. (See links below for current taxonomy.)
The families Cylichnidae and Scaphandridae have external shells into which they can partly withdraw.
The family Philinidae have completely enclosed fragile shells (partly exposed in Philine denticulata).
The anterior of the dorsum is a shovel-like cephalic shield and the posterior consists of a mantle covering the shell.
The foot (parapodium) has large parapodial flaps which extend up the flanks of the animal.
On most species there are no tentacles, and the gill is inside a mantle cavity.
Very little is known about their diet, but formaniferans, polychaete worms and juvenile molluscs have been recorded for some species. Some have stout gizzard plates for masticating food.
Some, at least, have a veliger larval stage.