Testate amoebae from freshwater ecosystems of the Sura River basin (middle Volga region). 2. Community structure

The species diversity and structure of testate amoebae communities inhabiting streams, rivers. lakes, and ponds from the Sura River basin were investigated. Local communities from silt and sand substrates are characterized by the lower level of the species diversity alternating communities from coarse debris sediments. The main factor affecting the species diversity is rather the type of water body than the type of substrate. The general distribution pattern of testate amoebae is rather uneven. However, the species complexes, which are tend to be (a) Difflugia pristis, D. lithophila, D. lingula, D. elegans D. hibiosa, D. urceolata, D. -rainen, Arcella rotillidata, Ceti trop yxis constricta from silt and sands (b) D. lintnetica. D. parva, D. corona, D. lanceolata, D. D. acut'ninata. D. cYlin(lrus, CN,cloln kahli from coarse debris sediments. Within the Sura River, three types of communities were distinguished: (I) the local community of the Upper Sura River with the predominance of Arcella species due to their close relations with acid boggy watec (2) the psarm-nophilous community with Ceti tropYxis species as dominants; (3) the silt community characteristic of the middle Sura River with the predominance of Arccfla rotittuhitei, Centropvri'v constricta, C. ecornis, D flhwia urceolata, D. liti-ithi, 1). labiosa. D. lacitstris, 0.gramen, D. pristiN, D. cle-ans, Net7ejj(j tj(bej-Cjjj(jttj.