The Paramecium aurelia species complex, frequency and co-occurrence across Europe

In Europe, 10 among the 15 known species of the Paramecium aurelia complex have been recorded including P. primaurelia, P. biaurelia, P. triaurelia, P. tetraurelia, P. pentaurelia, P. sexaurelia, P. septaurelia, P. novaurelia, P. dodecaurelia, and P. tredecaurelia. The occurrence of species of this complex in Europe has been estimated on the basis of the number of habitats and the ratio value (r.v.), i.e. the number of habitats for a defined species to the total number of habitats with species of the P. aurelia complex. The r.v. presents the relative frequency of the particular species to others of the complex. In total, 483 habitats were considered. The dominant species is P. novaurelia (r.v. 0.38, found in 186 habitats), followed by P. biaurelia (r.v. 0.26 in 125 habitats) and P. primaurelia (0.23 in 113 habitats). Other species are less frequent, such as P. tetraurelia (r.v. 0.06 found in 29 habitats), P. triaurelia (r.v. 0.04 in 22 habitats), or rare such as P. septaurelia (r.v. 0.025 found in 12 habitats), as well as P. pentaurelia and P. sexaurelia (r.v. 0.02 for both, found in 11 and 10 habitats, respectively). P. dodecaurelia was found in three localities in Europe (r.v. 0.006) and P. tredecaurelia is known from a single habitat (r.v. 0.002). This paper presents new populations, found at present, of species of the P. aurelia complex in Europe (Germany, Italy, Spain, Iceland, Poland, Great Britain) and one new from the USA.