Choanocystis rhytidos (Dürrschmidt, 1987) Siemensma, 1991
Diagnosis: Periplast, 35-40 µm in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. Spine scales, 9-12 µm long, bipartite, consisting of shaft and base-plate. Shaft cylindrical, 0.19 µm in diameter, presumably solid and slightly tapering towards the distal end, abrupt apically ending with 2-4 marginal teeth. Base-plate heart-shaped, 1.3 µm in diameter, Plate scales, 3.8-4 x 2.2-2.6 µm, elliptical or pear-shaped, ornamented by radially-arranged, branched furrows of different length. The area of the axial thickening and a narrow submarginal strip are smooth.
Distribution: Chile, New Zealand.
Remarks: A. rhytidos is common in Chile and New Zealand. Apart from the type locality it was found in samples from a semi-swamp forest on the shores of the Rio Oscuro, 35 km south of Puerto Montt, Chile, in swamps near Maramaranui, swamps near Lake Whangape, swamps aside the Manganahoe Lagoon, North Island, New Zealand and on the South Island in a swamp in the Buller Gorge. Temperature ranges from 7 to 12 °C, pH from 5.2—7.4, and conductivity from 20—800 pS25.