Gymnosphaera albida is free-living, usually benthic in shallow water. The cells are round and naked, around 70-100 μm in diameter, and resemble the unrelated Actinosphaerium. The outer cytoplasm, or ectoplasm, forms a distinct layer containing large vesicles.
Hedraiophrys hovassei is larger and lives attached to algae and other objects. The cells have a conical base, and are covered with long siliceous spicules. The ectoplasm is distinct and frothy, and typically contains bacterial and algal endosymbionts.
Actinocoryne contractilis is benthic. When feeding, it has a multinucleate base and a contractile stalk up to 150 μm in length, supporting a relatively small uninucleate head, where the central granule and axopods are located. It may move about in a headless amoeboid form. Reproduction is either by budding off the head or fragmentation of the headless form, producing small free-living cells similar to Gymnosphaera, which then attach themselves and regrow the stalk and base.
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