Spherical naked heliozoa with numerous small nuclei. A cytoplasm often has a discrete peripheral layer of large vacuoles, and the nuclei occur at the inner boundary of this layer. Axonemes terminate on the nuclei or an electron-dense material near the nuclei. We regard Camptonema of Schaudinn and Echinosphaerium of Hovasse as synonyms. With several species - type species A. eichhornii Ehrenberg, 1840.