English: Morphology of Cthylla microfasciculumque by differential interference contrast light microscopy. (A) Overall body plan of Cthylla cells showing shape and size, a posteriorly protruding axostyle and subanterior emergence of flagellar bundle. Flagella typically bundle during the forward stroke of the flagellar beat but even then dissociate at the tips (A–C). In the backstroke, the bundle substantially dissociates (D–E). When dissociated, five anterior flagella can be seen consistently (B and clustered arrowheads in C), and in many views a single recurrent flagellum is also evident around the axostyle protrusion (A & lone arrowhead in C). (F &G). Low magnification of a small flagellate observed in Heterotermes tenuis with a small bundle of anterior flagella and a robust protruding axostyle similar to those of Cthylla. According to molecular surveys H. tenuis harbours the closest known relative of Cthulhu, and we predict that the environmental sequence is derived from this flagellate. All scale bars are 10 µm.