Acanthocystis polymorpha

Acanthocystis polymorpha  Dürrschmidt, 1985

Diagnosis: Periplast 50—100 µm in diameter. Scales of 2 types. Protoplast unknown, all cells with photosynthetic symbionts as revealed by LM. Plate scales arranged in one to several compact layers, 4-5.5x 2.1-3.3 µm, ellipsoidal or ovoid, commonly with an approximately median narrowing. Plate scales asymmetrically or triangularly shaped have been observed, too. Usually they are uniformly thick without a clearly defined central ridge. Dorsal and ventral surfaces are smooth, sometimes revealing a delicate zonation caused by the successive apposition of scale material.

Spine scales of two types, all with tubular shafts and round plate-like bases. These base-plates possess ventrally a central annular depression and slightly rimmed margins. One type is 15-30 µm long, shaft not tapering, with slightly dilated distal ends, distal margins regularly indented. Second type is usually half as long as the other type, 5-10 µm, provided distally with curiously ‘funnel-like’ ends, caused by a considerably broadened shaft. There are 5-8 radially diverging rid­ges of which each terminates in a small pointed tooth. The scale material between has an slightly inwardly curved edge. The length of these spine scales varies between such extremes that there is sometimes even no shaft at all and the ‘funnel-like’ distal ends are directly attached to the base-plates. Transitional spine scales between both types are also present.

Ecology: Type habitat: Pools in a Sphagnum magellanicum bog, 12 km north of Castro, Island of Chiloe, Chile (1981).

Remarks: A. polymorpha bears some likeness to A. turfacea, for instance, in the possession of more than one kind of spine scale, in their similar base-plates, and in their tubular shafts. Apart from the type locality, A. polymorpha was also frequent in other Sphagnum bogs on Chiloe Islands, e.g. Sphagnum bog near Manao. It seems to inhabit especially acid, extremely oligotrophic, clear waters of low mineral content.

Single spine scales, perhaps belonging to A. polymorpha, have been published earlier by Takahashi (1959, PL VI, Fig. 49) from Japan, as microplankton no. 8 from Arasawa-dam.

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