Acanthocystis myriospina Penard, 1890, sensu Dürrschmidt, 1985
Diagnosis: Periplast, 10-45 μm in diameter (measurement based on whole mount), covered by 2 types of siliceous scales. Details of protoplast unknown. Plate-scales, 2.7-3.5 x 1.5-2.2 um, oviform to ellipsoidal. They are thin, with a sometimes blurred central ridge. Spine-scales of only one kind, 3.5-16 μm long, commonly extraordinarily numerous, with long, thin tubular shafts, plate-like bases (0.5-0.7 μm in diameter) and tridentate distal ends. The shaft narrows slightly towards its distal end.
Remarks: A. myriospina was described by Penard (1890) from material collected from stagnant waters in the vicinity of Wiesbaden, Germany. Apart from being some what larger (45 µm, measurement based on whole mounts, versus 30 µm) the most striking similarity between Penard’s diagnosis and the periplasts found in Chile are the extraordinary numerous spine-scales, which are long (about 2/3 or more of the cell diameter according to Penard) and delicate, straight or rarely curved. However, the distal ends of the spine scales are not tapering or pointed, but have three short teeth. This feature, however, is only visible by electron microscopy.
Beside those periplasts typical for A. myriospina, there have been others which should also be identified with A. myriospina as regards their identical scale structure. However, these deviate from the specific description in that their spine-scales are less numerous and the length of the shaft is considerably variable among single specimens from 3.5-16 μm. This suggests that these characteristics are of limited or no value for specific identification, in contrast to the scale structure itself.
Neotype: deposited in the British Museum London, Protozoa Section (accession no. 1983: 1: 31: 2).
Geographical distribution: Freshwater. Habitat of the neotype: Small forest pond near Entre Lagos on the Puyehue pass road. Collected on July 20, 1981. Previous records, based on LM observations: Geneva, Switzerland (Penard 1901, 1904), Spitzbergen (Penard 1903), and England (Cash and Wailes 1921).
