Pyramidellidae

Pyramidellidae is a family of small to very small marine gastropod mollusks in the superfamily Pyramidelloidea. Commonly known as pyrams, members are ectoparasites that feed on invertebrates rather than by grazing. The group is diverse, with hundreds of described species and many genera, including the type genus Pyramidella and the well-known Odostomia.

Anatomy and shells: Most species have a slender, elongate conical shell with numerous whorls. The protoconch is often heterostrophic, with the initial whorls oriented differently from the rest of the shell. The aperture is typically elongated and the outer lip simple; the inner lip features a characteristic fold or plication on the columella. Most pyramidellids lack a radula, and many possess a small calcareous operculum.

Ecology and feeding: Pyramidellellids are ectoparasites, feeding via a tubular proboscis that extends to the hosts and sucks fluids or tissue. Their hosts are diverse and include other mollusks and polychaete worms. Reproduction is sexual, with separate sexes in many species, and larval development varies among taxa.

Distribution and diversity: The family is cosmopolitan, found in marine environments from shallow subtidal zones to the deep sea. They have a long fossil record dating back to the Cretaceous. With numerous genera and many described species, Pyramidellidae is of interest to marine biologists and paleontologists for its diversity and parasitic ecology.