Korotnevella pelagolacustris Van Wichelen & Vanormelingen, 2016

 

Diagnosis: Locomotive form dactylopodial with a length of 20–65 µm and a width of 6–32 µm. Vesicular nucleus about 6 µm in diameter with one slightly eccentrically located nucleolus. Floating form radial, maximally 25 µm in diameter, with up to 20 pointed pseudopodia. Scales elliptical, disk-shaped with a length of 260–391 nm and a width of 153–206 nm carrying a central spine 98–163 nm in length. Cyst formation rarely observed. Amoebae occasionally aggregate during cultivation.

 

Ecology: Freshwater. It feeds voraciously on Microcystis aeruginosa. No growth was observed when offering other Microcystis morphotypes (M. viridis, M. wesenbergii), heterotrophic bacteria and green algae (Acutodesmus) (Van Wichelen et al. 2012, Van Wichelen, unpublished).
Type locality: Strain A16WVB was isolated from a Microcystis bloom sample from a small, eutrophied urban pond in Westveldpark, Sint-Amandsberg (Gent, Belgium). Other strains were isolated from the same locality and from a Microcystis bloom in Lake Mälaren (Ekoln, Sweden). Very high densities of a morphological similar amoeba were found in Microcystis bloom samples (06/07/2015) from a fishpond in Zandhoven (Belgium).

 

Differential diagnosis: K. pelagolacustris closely resembles K. diskophora (Smirnov 1999), the only described Korotnevella species so far with disc-like scales on its cell surface (basket or crown-like shaped or more than 1 scale type in all other Korotnevella spp.). However, K. diskophora is smaller in size (16–34 µm, mean 23 µm) and has smaller spines (about 80 nm) on its scales. Moreover, the floating form of K. pelagolacustris is globular with up to 20 radiating thin pseudopodia while the one described for K. diskophora is irregular with 1–4 long thin, tapering pseudopodia. Both species also differ in their ecology. K. diskophora was isolated from bottom sediments of the small freshwater Lake Leshevoe in North-Western Russia where it feeds on bacteria while K. pelagolacustris is isolated from Microcystis blooms in eutrophied water bodies where it specifically feeds on the cells of certain Microcystis colonies (Van Wichelen et al. 2010, Van Wichelen unpublished). K. jeppesenii, the other newly described species with the same ecology as K. pelagolacustris, is clearly smaller in size (max. 41 µm), has smaller (max. 327 nm), relatively wider (mean L/W ratio 1.6) disclike scales with shorter spines (max. 97 nm) and differs in 18S rDNA sequence.