Shell of limpet form; outline irregular; with septum or deck formed by columellar border of aperture. Early teleoconch with traces of spiral sculpture strongly or weakly represented or lacking. Operculum lacking. Head and neck long, flattened, bearing cephalic lappets; tentacles short, eyes at bases. Mantle cavity deep, filaments of ctenidium modified for filter feeding, tips of filaments overlying food groove leading to mouth.
Biology. Calyptraeids are sedentary limpets with unique modifications of the ctenidium and mantle cavity for filter feeding. The shell conforms to the area of attachment. All are protandrous hermaphrodites, starting as male and changing to female as larger sizes are attained.
Remarks. Genera are distinguished by placement of the septum and amount of coiling retained. Genera that retain the most coiling in the teleoconch are considered the most primitive in the family.

Calyptraeid shells are low and conical, distinguished by the presence of an internal shelf or deck. Calyptraeids are sessile ciliary feeders, and they brood their young. Two genera are represented in Hawaiian waters: Crepidula, the slipper shell, with a flat deck across one half of the shell aperture, and Crucibulum, the cup and saucer limpet, with an internal, cuplike projection.