The Aplustridae was known by the name of Hydatinidae until recently. They are large and very conspicuous bubble shells due to their bright colours, flamboyant and enlarged foot and spirally banded shells.
The thin, external shell is without a spire, ovoid or globose in shape with a large aperture but even so the animal cannot withdraw completely inside its shell. It therefore does not possess an operculum.
There is a large head shield producing a pair of broad and long posterior lobes framing the close set eyes anteriorly. With anterior lobes folded laterally the whole effect of the head is like that of a mask.
The posterior end of the mantle produces a large infrapallial lobe folding up and over the apex of the shell.
The foot is broad and delicate, and the sides are enlarged into what could be described as “unfurled parapodia”.
At times the large plicate gill may be visible protruding from the mantle cavity on the right side.
All Aplustrids feed on polychaete worms