Pyramidellid

Pyramidellid refers to a family of small to minute marine gastropods in the family Pyramidellidae, within the superfamily Pyramidelloidea. They are ectoparasitic on other invertebrates, especially molluscs and polychaete worms, and occur worldwide in marine environments ranging from shallow coastal waters to deep seas.

Morphologically, pyramidellids have elongated, conical shells with many whorls. The aperture is typically oval, and the outer lip is often simple. Shell surface may be smooth or finely sculptured with axial or spiral lines. A characteristic feature is the heterostrophic protoconch, where the initial whorls are oriented differently from the later ones. The columella often bears a prominent fold or folds, which can help in identification.

Ecology and feeding habits are distinctive: pyramidellids lack a true radula and feed using a long proboscis to pierce or suck fluids from their hosts. They are primarily ectoparasites on other invertebrates, including molluscs, polychaetes, and sometimes echinoderms. Most species are very small (micromolluscs), and they can be overlooked in ecological surveys.

Taxonomy and diversity are complex. The family contains many genera, including Odostomia and Pyramidella, among others. Classification within Pyramidelloidea has been refined with molecular data, and the exact number of species remains uncertain due to ongoing revisions and the small, sometimes cryptic nature of many members.

Significance and distribution: pyramidellids contribute to marine biodiversity and host–parasite interactions in various ecosystems. They have a long fossil record, with representatives known from the Cretaceous and later, reflecting their long-standing presence in marine faunas.