Spatangoidea

‖Spat′an‐goi″de‐a (?), n. pl. [NL. See Spatangus, and -oid.] (Zoöl.) An order of irregular sea urchins, usually having a more or less heart-shaped shell with four or five petal-like ambulacra above. The mouth is edentulous and situated anteriorly, on the under side.