A class of marine planktonic chromists. Their skeletons are composed of hollow, siliceous rods and (see illus.), resemble those of the Radiolaria, with which they have been grouped. They are usually subpyramidal or hemispherical in shape, delicately filigreed, and range in size from 10 to 150 micrometers. Two families and 11 genera of silicoflagellates have been described from siliceous sedimentary rocks ranging in age from the early Cretaceous to Recent, in association with abundant diatoms and siliceous sponge spicules, however, this may change pending systematic revision. One genus, Dictyocha, lives in the ocean today.