\Spat`an*goi"de*a\, n. pl. [NL. See {Spatangus},
and {-oid}.] (Zo["o]l.)
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.