Scrippsiella acuminata (Ehrenberg) Kretschmann, Elbrächter, Zinssmeister, S. Soehner, Kirsch, Kusber et Gottschling

(Figures 26–28)

Cells were brown in colour with a pale central nucleus (Figure 26) and 21–26 µm long and 20–28 µm wide. Cells had a conical epitheca and a rounded hypotheca and were circular when seen in apical view (Figures 26 and 27). The cingulum was median and only slightly offset. Characteristic cysts were formed in one isolate (Figure 28). One Caspian and one Black Sea isolate were successfully sequenced and placed in the tree alongside Scrippsiella trochoidea (F. Stein) Loeblich III (considered a heterotypic synonym of S. acuminata by Kretschmann et al. 2015) from the Lafeyette River in the USA (Figure 32). Two other Scrippsiella species are of note to review here – S. plana and S. spinifera Honsell et Cabrini. In their paper describing S. plana from the Caspian Sea for the first time, Luo et al. (2016) clearly illustrate both species which each have characteristic motile cells. Scrippsiella plana has a distinctive flattened morphology and S. spinifera an elongate morphology with small antapical spines. The cultures developed in this study did not show these thecal morphologies; furthermore, a sequenced isolate formed characteristic S. trochoidea cysts. The taxonomy of Scrippsiella sensu lato remains enigmatic with further resolution awaiting sequencing of key species (Luo et al. 2016).