The species Coleps viridis was established by Ehrenberg in 1831, but later considered as a form of Coleps hirtus by Kahl and named Coleps hirtus viridis. It was not until 2021 that Pröschold et al. subjected Coleps hirtus viridis to morphological and genetic analysis, including symbiotic algae. As a result of the study, Pröschold et al. re-established the original name Coleps virdis and were able to identify the symbiotic algae as Micractinium conductrix.

In my population all specimens of Coleps viridis were smaller than 50 µm. Because of the small size the species is probably often overlooked or confused with Coleps hirtus or Coleps hirtus var. minor. At low magnifications the cells appear opaque black. Only at higher magnifications the green coloration becomes visible due to the symbiotic algae (s. figs. 1 a-d and 2 a-c). I could count 15–30 symbiotic algae in each cell. The algae cells have a cup-shaped chloroplast with a pyrenoid, are spherical and have a diameter of about 5.0 -5.4 µm (s. fig. 3). Thus, they correspond to the description of Micractinium conductrix by Pröschold et al. Coleps virdis has one caudal cilium (s. figs. 1 c and 2 a-b) and the armour is of the Coleps hirtus type. That means each main plate has 4 “windows” which are pretzel-shaped (s. fig. 4).