Choanocystis pelagica (Ostenfeld, 1904) Mikrjukov, 1994
Syn.: Acanthocystis pelagica Ostenfeld, 1904
Diagnosis: Cells are 25–40 µm in diameter with plate-scales and one type of spicules in the periplast. Spicules are about 7 µm long; the shaft is hollow, cylindrical, about 0.4 µm in diameter, slightly is curved towards the heart-shaped base-plate, 1.5–1.8 µm in diameter, and abruptly tapered towards the pointed apex; the base-plate is covered by numerous fine granules. Plate-scales are4.0–5.0 x 2.0–2.5 µm, with a well-developed medial constriction, up to 1.7–2.0 µm wide, patternless, surrounded by a thin curved marginal rim.
Ecology: Marine. Northern Sea, White Sea.