Phylum: Chlorophyta   Family: Scenedesmaceae

Comasiella arcuata (E. Lemmermann) E. Hegewald, M. Wolf, A. Keller, T. Friedl & L. Krienitz 2010

First described by Lemmermann (1898: 150) as Scenedesmus bijugatus var. arcuatus. Soon after he moved it to Scenedesmus arcuatus Lemmermann 1899: 112, pl. I 1: 2-4) with illustrations. More recently it was renamed by the current authors.
Cell dimensions: L: 7-18 µm, B: 3-9.5.
Status unknown in the Outer Hebrides but probably not uncommon in slow-flowing waters.

References: 
Hegewald, E., Wolf, M., Keller, A. Friedl, T. & Krienitz, L. (2010). ITS2 sequence-structure phylogeny in the Scenedesmaceae with special reference to Coelastrum (Chlorophyta, Chlorophyceae), including the new genera Comasiella and Pectinodesmus.
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition). The Freshwater Algal Flora of the British Isles. Lemmermann, E. (1899). Das Phytoplankton sächsischer Teiche.