spatangoidea
Spat`an*goi"de*a, n. pl. Etym: [NL. See Spatangus, and -oid.] (Zoöl.) Defn: 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.