Koliella

Koliella consists of straight or curved spindle-shaped or needle-shaped cells. The apices may be rounded, obtuse, acute, or sharply pointed. Cells contain a single parietal chloroplast lining the inside of the cell, which may be straight or spiraled; a pyrenoid may be present or absent. Oil droplets are also present within the cell.^[5]

Koliella reproduces vegetatively by cell division; cells usually detach after division, but may occasionally be found in short chains. It is similar to a number of fusiform green algal genera, such as Monoraphidium, Ankistrodesmus, and Schroederia but the cell division is transverse, dividing into two shorter cells.^[7] It also reproduces asexually by producing zoospores, which are biflagellate. Sexual reproduction occurs in this genus, and is oogamous, but not much details are known.^[5]

Koliella is similar to the genus Raphidonema, and is primarily distinguished from the latter genus in that its cells detach after division (while Raphidonema forms filaments of cells).^[5] Some taxonomists suggest that the difference between the two genera is too small to warrant separation, and that Koliella should be considered a synonym of Raphidonema.^[1] For example, filaments of Raphidonema often separate into single cells akin to Koliella when placed in a liquid medium.^[8]

As currently defined, the genus Koliella is polyphyletic; the type species K. spiculiformis is closely related to Chlorella while other species (K. longiseta and K. sempervirens) appear to be more closely related to Stichococcus.^[9]