Genus Acanthocystis Carter, 1863
Diagnosis: Centrohelea with a periplast with tangential plate-scales and external radial spine-scales. Radial spine-scales with a cylindrical shaft, attached to the central part of a radially symmetrical base-plate.
Type species: Acanthocystis turfacea Carter, 1863
Remarks: The type species A. turfacea Carter, 1863 has been recorded in both marine, brackish, and fresh waters. Most other species occur in fresh waters.
Reference: Siemensma (1991)