Diagnosis: Locomotive form fan-shaped. Cell length during locomotion 15–57 µm (mean 35), width 13–64 µm (33) and length/width ratio 0.4–2 (1.1). Vesicular nucleus 2–7 µm in diameter with one centrally located nucleolus. Floating form usually radial and symmetric with 5–11 pointed pseudopodia that are basally thickened. Cysts elliptical to ovoid, up to 32 µm in diameter.

Feeding behavior: Feeds voraciously on Microcystis aeruginosa cells (see Van Wichelen et al. 2012) although growth is also sustained on heterotrophic bacteria and pico-cyanobacteria (Van Wichelen, unpublished).

Type material: Strain A2FBB is designated as type strain. It is available from the NIES Microbial Culture Collection (NIES-3728). The 18S rDNA GenBank accession number is KP719193. Other strains are A4P-4ZHB, A2SMB, A1DVDPB, A2DVDPB and A3DVDPB (NIES-3765).

Type locality: Strain A2 FBB was isolated from a Microcystis bloom sample from a ditch surrounding a moat (Fort Bornem, Belgium) (Table1). Other strains were isolated from Microcystis blooms in fish ponds in Zonhoven and in De Panne and in a recreational lake (Schulensmeer, Lummen), all located in the Flemish part of Belgium.

Etymology: planctonica referring to its planktonic life style.

Differential diagnosis: V. lata cells are always flabellate and the hyaline area occupies a larger proportion of the cell (⅔) than in V. planctonica (40%). V. miroides is smaller (<35 µm), contains crystals in its cytoplasm and has a more extended hyaline area (> ½ body length) surrounding the whole cell (Page 1988, Smirnov et al. 2007). V. simplex is much larger in size (on average 42–52 µm) and has usually fecal pellets adhered to the cell (Page 1988, Smirnov et al. 2007), a feature never observed in V. planctonica. The 18S rDNA sequence distinguishes V. planctonica from all other Vannella species currently present in GenBank.