[ ˌreɪdɪə(ʊ)'lɛ:rɪən ]
■ noun Zoology a single-celled aquatic animal having a spherical amoeba-like body with a spiny skeleton of silica. [Many species in the phylum Actinopoda.]
Origin
C19: from mod. L. radiolaria , from late L. radiolus 'faint ray', dimin. of radius 'ray'.