Little-known and new heliozoeans: the centrohelid genus Acanthocystis, including descriptions of nine new species

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Abstract
Thirteen species of the heliozoean genus Acanthocystis have been found in Ontario lakes and ponds and were studied with optical and transmission electron microscopes. Nine of these species are described as new. All species possess silicified plate-scales and spine-scales, the morphology of which is taxonomically reliable. There exist two well-defined morphotypes within the genus; the most common includes those with spine-scale bases in the form of a shallow saucer, with or without a cleft. The second type includes those with a spoon-shaped membrane fused to the bent proximal portion of the spine shaft. Aspects of cell function relating to the nucleus, contractile vacuoles, "zoochlorellae," and axopodia are also discussed.