Two New Species of Centrohelid Heliozoans: Acanthocystis costata sp. nov. and Choanocystis symna sp. nov. Author Zlatogursky, Vasily V. text Acta Protozoologica 2014 53 4 313 324 https://www.mendeley.com/catalogue/bf9b6251-8f7a-37a4-af28-d3023e35cd6d/ journal article 10.4467/16890027AP.14.021.1776 1689-0027 10371188 Choanocystis symna sp. nov. ( Figs 3 , 4 ) Diagnosis: Cell body ca. 6.7 µm in diameter. Axopodia three–five times longer than a cell diameter. Plate scales dumbbell-shaped with a median constriction. Circlular lines, parallel to the border of the scale sometimes can be seen. The shafts of spine scales can be straight, but usually it is slightly curved towards the scale base. Length of plate scales 4.4–5.0 µm (ca. 4.7 µm); width 1.62–1.90 µm (ca. 1.71 µm). Spine scales with heart-shaped bases. Sometimes a small circular depression is located on the base at the place of the shaft location. Distal ends of spine scales bear from three to five (usually four) short teeth. Length of spine scales 3.9–6.7 µm (ca. 5.1 µm). Cells tightly attach to the bottom of Petri dish or, very rarely, float. No rolling movement was observed. Etymology: The species–group name symna refers to the name of type location – Lake Symniakhovskoe. Type locality: Lake Symniakhovskoe , Valamo island , North-Western Russia , 61°22′912″N, 30°58′503″E. Collected 03.08.2010 . Culture: CCAP 1597 /1 – the clonal culture from which type material and all the data provided in this paper were obtained . Hapantotype: preparation ( Fig. 3 ) has been deposited in the Natural History Museum UK , accession number NHMUK 2013.6.28.1. Type sequence: GenBank accession number KF990487. ZooBank LSID : urn:lsid:zoobank.org:act: C538EF 0A-BF25-4539-8C62-CACE552B9C97 Comparative diagnosis: There are only two more described species of Choanocystis with dumbbell-shaped plate scales and teeth-bearing spine scales: C. pantopoda and C. aculeata . C. aculeata is a much larger heliozoan (cell diameter 23–60 µm) and has very different spine scales which are notably tapering and have short protrusions (“nodules”) in proximal part of the shaft. This species also has from five to eleven teeth on the spine scale tip ( Dürrschmidt 1985 , Siemensma and Roijackers 1988 ). C. pantopoda spine scales are three times longer than plate scales, while in C. symna only two times longer. The length of scales is 25–30 µm in C. pantopoda , while in C. symna it is only about 5 µm. The number of teeth in C. pantopoda is four to six ( Siemensma 1991 ), but six teeth have never been observed in C. symna .