Acanthometra; An order of Acantharia. These marine protozoans have a skeleton limited to 20 radially arranged rods which extend from the center, forming a characteristic pattern in which angles are quite exact, as in Acanthometra. The cytoplasm surrounding the spines contains a conical array of contractile microfila-ments (myophrisks or myonemes) that act to expand or contract the gelatinous sheath surrounding the cell, a phenomenon that is apparently responsible for changes in the level of flotation. See also Acantharia; Actinopodea; Protozoa; Sarcodina; Sarcomastigophora.