A class of Sarcodina; or in some modern schemes a superclass (Actinopoda) within the phylum Sarcomastigophora. Some of these protozoans have more or less permanent pseudopodia, composed of a central shaft of microtubules surrounded by a thin cytoplasmic envelope (axopodia); others have delicate and often radially arranged filopodia (filamentous, flexible pseudopodia) or filoreticulopodia (filamentous, branched pseudopodia) without axial microtubules. Although some are stalked and attached to the substratum (sessile), most are floating types. There are four subclasses: Radiolaria (Polycystinea and Phaeodarea), Acantharia, Heliozoia, and Proteomyxidia.