Dimensional characteristics of Trachelomonas volvocina (Ehrenberg) Ehrenberg from Irtysh river middle reaches plankton

Measured diameters of 153 houses of Trachelomonas volvocina (Ehrenberg) Ehrenberg Euglena algae from the Irtysh River middle reaches plankton (near the Omsk city) for open-water periods of 2014 and 2015. Found specimens with houses diameter of 5.0 μm at the spring and summer seasons, but according to the qualifier books, the smallest diameter of the T. volvocina house is 6.0 μm. Registered specimens with house diameter of 5.0-11.0 μm during open-water periods of 2014 and 2015, the highest occurrence frequency had houses with diameter 6.25-7.5 μm. Calculated average diameter and volume of the T. volvocina house by seasons and during the open-water period. The average for two years house diameter was 7.11 ± 0.09 μm, volume - 201.94 ± 8.13 μm³. The widest variation T. volvocina size was observed at the spring season. No significant differences between the dimensional characteristics T. volvocina detected for 2014 and 2015. Found statistically significant difference between the T. volvocina house sizes in spring and autumn for the 1 % significance level. The maximum average house size was registered at the spring season and decreased during the open-water period. Found that T. vol-vocina house is larger at spring than the fall, an average, by 0.64 μm for diameter and 60.45 μm 3 for volume.volvocina cells size reduction is associated with the high eutrophication degree and pollution of the Irtysh River middle reaches by heavy metals.