Not perforated; having no perforations, foramina, or pores; atresial; in zoology, specifically, of or pertaining to the Imperforata.As applied to the shells of the gastropod Mollusca, having the inner parts of the whorls coalesced into a columella leaving no opening or perforation. In the Echinoidea, or sea-urchins, the mamelons which support the spines are imperforate when not pierced by a central foramen.