any single-celled freshwater algae of the family Desmidiaceae, characterized by a division of the body into mirror-image halves joined by a bridge containing the nucleus, and having a spiny or bristly exterior: sometimes forming into colonies or branching filaments.
Origin: 1860–65; < Neo-Latin Desmidium a genus of the family < Greek desm(ós) a band, chain (compare deîn to fasten) + Neo-Latin -idium-idium