Acanthocystis siemensmae, Gerasimova & Plotnikov, 2016

Gerasimova, Elena A. & Plotnikov, Andrey O., 2016, New Freshwater Species of Centrohelids Acanthocystis lyra sp. nov. and Acanthocystis siemensmae sp. nov. (Haptista, Heliozoa, Centrohelea) from the South Urals, Russia, Acta Protozoologica 55 (4), pp. 231-237 : 233-235

Acanthocystis siemensmae sp. nov. ( Figs 2 , 3 D–F )

Diagnosis: Cells are 17.0–21.0 µm (mean 19.0) in diameter. A cell coat consists of plate scales of a single type and spine scales of two types. The long spine scales have narrow, hollow shafts 6.5–10.8 μm long. The shaft is slightly branching towards the apex and has 14–16 teeth. Extended part of the apex contains four symmetrically oriented longitudinal ridges; each ridge is ended by four teeth of different length. Two central teeth of the ridge usually are longer than lateral ones. Basal plates of the long spine scales are circular, 0.9–1.2 μm in diameter. The short spine scales are 1.6–2.9 μm long with narrow shafts and expanded cup-shaped apices up to 1.9 μm in diameter. The apex looks like a maple leaf due to division onto 3–5 ridges of irregular shape. Each ridge has a few teeth of different length. Basal plates of the short spine scales are circular, 0.6–1.0 μm in diameter. The plate scales are plane, patternless, elliptical or pearshaped with a thin marginal rim. Length of the plate scales is 2.5–4.4 μm, width 1.2–2.7 μm.

Comparisons with similar species: A. siemensmae is slightly similar to A. pectinata Penard, 1889 , A. polymorpha Dürrschmidt, 1985 and A. nichollsi Siemensma et Roijackers, 1988 , in structure of the cup-shaped apex of the short spine scales. The short spine scales of A. pectinata have 4–6 short teeth; the long spine scales have 2–3 teeth. In contrast, A. siemensmae has the short spine scales with 3–5 ridges; each of them is ended by a few teeth. Its long scales possess 4 ridges and 14–16 teeth. In addition, plate scales of A. pectinata are ornamented by granules, whereas those of A. siemensmae are patternless.

The short spine scales of A. polymorpha possess 5–8 ridges ended with one tooth, while A. siemensmae has the short spine scales with 3-5 ridges, each of them with a few teeth. The long spine scales of A. polymorpha have slightly dilated distal ends with teeth. In contrast, the distal ends of the long spine scales of A. siemensmae reveal four ridges with terminal teeth.

Short spine scales of A. nichollsi have a flared termi- nus consisting of six spine-like ribs joined by a membrane with a scalloped margin, whereas the short spine scales of A. siemensmae are ended by 3–5 ridges with a few apical teeth. The long spine scales of A. siemensmae have 4 ridges with teeth, while ones of A. polymorpha have slightly dilated distal ends with teeth. The plate scales of A. nichollsi are elliptical and ornamented with a medial thickening, radial ribs and a marginal rim, whereas the only ornamentation on the plate scales of A. siemensmae is the marginal rim.

Etymology: The species group name siemensmae is proposed in honor of an authority on several groups of amoeboid and heliozoan protists Ferry Siemensma.

Type locality: Bottom sediment from the Pismenka River , Kidryasovo settlement, the South Urals, South- East of European part of Russia, 51°15′41N, 57°28′42E. Collected 11.05.2014 .

Hapantotype: Preparation #50 ( Fig. 2 ) has been deposited in the Laboratory of Microbiology, Institute for Biology of Inland Waters of Russian Academy of Sci- ences (Borok, Russia).

ZooBank LSID: urn:lsid:zoobank.org:act:9CA717BA-97AE-4593-B69C-D9C6C05F615B

Figures

Fig. 2. SEM of Acanthocystis siemensmae sp. nov. A – General view of the scales. B – Long spine scales. C – Apices of long spine scales with ridges. D – Plate scale, long and short spine scale with basal plate. E – Apices of short spine scales with ridges. F – Ridges with teeth at the apex of short spine scale. G – Plate scale with marginal rim. Abbreviations: bp – basal plate; ct – central tooth; ls – long spine scale; lt – lateral tooth; mr – marginal rim; ps – plate scale; r – ridge; sh – shaft; ss – short spine scale; t – teeth. Scale bars: A – 10 µm; B, C, E, G – 1 µm; D – 2 µm, F – 0.5 µm.

Fig. 3. Line drawings of scales of Acanthocystis lyra sp. nov. (A–C) and Acanthocystis siemensmae sp. nov. (D–F):A, D – long spine scales; B, E – short spine scales; C, F – plate scales.