Choanocystis curvata Cavalier-Smith and von der Heyden, 2007
Diagnosis: cell size 15 µm. Radial scales (3-5 µm long) morphologically most similar to those of C. lepidula (Penard, 1904) Siemensma and Roijakers, 1988 and C. pelagica in their shaft being smoothly curved towards the main basal disc and away from its invagination (unlike C. kareliensis where it is basally curved towards but distally away from the basal disc), though sometimes it is straighter or more irregularly curved. Differs from C. pelagica in the shaft not being pointed but truncate (and the base lacking surface granules); shaft tip differs from C. lepidula in having two or three marginal teeth as in C. perpusilla (perpusilla, one of only two species with similar length scales, differs by having a straight shaft and in lacking the strong indentation in the basal disc, as well as possessing only two marginal teeth; the other, rossica, has straight shaft lacking teeth and proportionally much wider base plate). Basal plate scales 2-3 µm long: oval with a very slight indentation on one side, lacking radial furrows, with oval central thickening that is much less elongated as a central rib than in any other Choanocystis. C. rotundata differs by having a straight shaft on its radial scales with numerous apical teeth and a highly elongate radial ridge on its plate scales. Other species have radically different shafts (sometimes branched) or heavily bilobed plate scales.
Type locality: Harrison Hot Springs, British Columbia, Canada.