Ancyromonas sigmoides Kent 1880 (Figs 2a, 3a)

Cells are 3–5 µm long, oval shaped and dorsoventrally flattened. The thin anterior flagellum is emerging from an anterior depression and is beating slowly. The non-acronematic trailing posterior flagellum is about 1.5 times the cell length. The cells move by gliding. Description is based on the observations of 19 cells. Occurance: every month at Acı Lake, temperature 1–23.5 °C, salinity 24–67.5 psu, dissolved oxygen 3.75–13.2 mg /L.

Remarks: Detailed studies of the genus Ancyromonas were published by two separate groups (Cavalier-Smith et al. 2008; Heiss et al. 2010, 2011). According to the work of Heiss et al. (2010), Planomonas Cavalier-Smith et al. 2008 has been concluded as a junior synonym of Ancyromonas . According to the previous studies (Heiss et al. 2010, 2011; Lee 2015), the genus Ancyromonas consists of 6 nominal marine ( A. sigmoides, A. cephalopora, A. impulusive, A. melba, A. sinistra, A. micra) and 2 nominal freshwater ( A. howeae, A. limna) species. When compared to Ancyromonas sigmoides, A. melba is larger, A. sinistra has a margin with the presumptive extrusomes and having a flatter cell body. Ancyromonas micra has a thicker anterior flagellum and a bigger rostrum, whereas A. howeae and A. limna have a contractile vacuole. As mentioned by Aydın and Lee (2012) due to their morphological similarities, Ancyromonas micra might have been reported elsewhere under the name of A. sigmoides . Ancyromonas sigmoides is similar to Metopion fluens, but is distinguished by the anteriorly directed flagellum. In addition, the second flagellum of M. fluens is thicker and is directed to the rear. This species has a worldwide distribution.