[2] A tubular gullet lined with usually two rows of ejectisomes is found to be in the posterior region of the cell.

A single plastid and nucleomorph are present, with it possessing the biliprotein pigment Cr-phycoerythrin 555 or one of Cr-phycocyanin, 577, 612 and 630.

The periplast of H. brunnescens has crystalline plates and an unusual secondary layer composed of small "sausage-like" fibrils.

[1] Hemiselmis species may easily be overlooked in samples due to their small size and rapid movement, but can be recognized by the special corkscrew swimming motion.

[1] It is concluded that the spiral swimming is not because of the irregularity in length or structure of flagella, but because of the dorsoventral flattening of its body.

Also, the fact that the flagella are attached at a low point near posterior contributed to the unique swimming pattern observed.

Using pulsed-field gel electrophoresis (PFGE), size of the H. rufescens nucleomorph genome was estimated to be 580 kb.