Choanocystis pertusa (Dürrschmidt, 1987) Siemensma, 1991
Diagnosis: Periplast, 50-60 µm in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales, 15-25 µm long, consisting of shaft and base-plate. Shaft, 0.2 µm thick, apparently solid or only partly hollow. Spines slightly tapering towards the distal end, apex with 4 marginal teeth. Shaft seated eccentrically to a heart-shaped base-plate, 1.4 µm in diameter. Plate scales, 5.6-6 x 3.3 µm, elliptical, sometimes slightly curved. Scale ornamentation consists of n µmerous radial slits, 0.56 µm long and 0.07-0.14 µm wide, directly situated on both sides of the axial thickening, which is 3.0 µm long. Rest of the scale smooth.
Remarks: It is not possible to distinguish between C. granulata and C. pertusa with reference to the spine scales alone, though these of C. pertusa are 1/4 longer than those of C. granulata. The slit-pattern on the otherwise smooth plate scales, is the most characteristic feature of C. pertusa and plate scales are about twice as large as those of C. granulata.
Geographical distribution: Sri Lanka.