With plural (or occasionally singular) agreement: a phylum of amoeboid protozoans comprising the ‘radiolarians’ and heliozoans, characterized by a spherical body with radiating axopodia. Also with plural agreement: protozoans of this phylum (collectively or individually).
Formerly regarded as a class, superclass, or subphylum, this group is probably polyphyletic and is still under review.
Late 19th century (in an earlier sense). From scientific Latin Actinopoda from ancient Greek ἀκτινο- + scientific Latin -poda.