The pyram family is distributed worldwide with more than 6,000 named species in more than 350 nominal genera and subgenera.

There is an absence of a general consensus regarding which species belong to a specific genus or subgenus, contributing to much confusion.

The shell of these snails has a blunt, heterostrophic (i.e. whorls appear to be coiled in the opposite direction to those of the teleoconch) protoconch, which is often pointed sideways or wrapped up.

The operculum is ovoid and paucispiral, with the apex anterior, a thread-like arcuate ridge on the proximal side, the inner margin notched in harmony with the plaits of the pillar when prominent.

The species are characterized by the lack of jaw or radula, because they are ectoparasites (mostly on polychaetes or other molluscs).

[14][15] A few species in the family Pyramidellidae, such as Otopleura mitralis, are symbiotic with sea anemones, such as Neoaiptasia morbilla.

Instead their long proboscis is used to pierce the skin of its prey and suck up its fluids and soft tissues.

Between the head and the propodium (the foremost division of the foot), a lobed process called the mentum (= thin projection) is visible.