Gastrotricha of alder woods in western and eastern Poland have been investigated. 48 species were recorded. Aspidiophorus slovinensis has been found for the second tim e, whereas Chaetonotus octonarius -for the first tim e in Poland. The fauna of alder wroods has a great specific variety, the m ost abundant species being Heterolepidoderma gracile. Also abundant are the species of the fam ily Dasydytidae. G. Kisielewska, J. Kisielewski qualitatively analysed m aterial on Petri dislies was

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... d till the last gastrotrich was caught. Thus, in calculations of individual dominance (D) and general diversity index (H ') hoth the results of quantitative and qualitative investigations could be used. However, the paper contains among others results of investigations between 1972 and 1975, when individuals were caught selectively from the dish but of course these data were not used in calculations of individual dominance and diversity index. Sim ilarly as in other papers of the series som e samples parented aquarium cultures, in which Gastrotricha were exam ined for a longer period of time. Thus obtained results enriched the list of species, but they could not be taken into consideration when giving the phenological data. The list of months in which particular Gastrotricha occur, given in the review of species, is based on the id en tifi cations of these species during 48 hours after sampling. M ATERIAL AND RESEARCH A R EA Alder woods are a habitat of swam py forests w ith the prevalence of alders (Alnus spp.). They are accompanied, mainly in north-eastern Poland, by birches (Betula spp.) and spruce (Picea abies). In the abundant undergrowth of forest floor very im portant are the high sedge associations (Magnocaricion). Peat-m osses are not a typical vegetation component. The floor of a typical alder wood has a spatial structure differentiated into hummocks and valley mires. In this environm ent there arc great fluctuations of water level; in spring tliero is usually a water level among trees, and in drier alder woods there are at least some pools. In summer and autumn this habitat gradually dries up and the surface waters disappear entirely or partly. The studies were conducted between 1972 and 1975, and between 1981 and 1984, in the latter period more regularly. Samples were taken between March and April, and between June and September. On the whole 29 samples were taken consisting of 1-5 sub samples, depending on the surface area of alder wood and the existing water conditions; 7 of these sam ples were quantitative ones. Samples were taken from the following localities (see also the map): 1. Ciechocin, commune Cekcyn, Bydgoszcz province. Small, rather dry alder wood w ith abundant high sedge vegetation but w ithout a fully formed hum mock structure. 1 qualitative sample. 2. Murucin, commune Sicienko, Bydgoszcz province. Typical but sm all alder wood, usually swam py and surrounded by meadows. 1 qualitative sam ple, afterwards aquarium culture. 3. Pobiedziska surroundings, Poznań province. Freshly cut alder wood w ithout a hum m ock structure. 1 qualitative sample. 4. W łocławek surroundings, close to road E 16, near the kilom etrepost 119. Small alder wood w ithout typical vegetation. 1 qualitative sample, afterwards aquarium culture. 5. Niezgoda, commune Żmigród, W rocław province. Part of a vast alder wood com plex to the right of the road from Milicz to Żmigród. Typical vegetation and structure. There was an exceptional drought (August 1983) when sam pling and the m aterial was taken from sm all hollows, where there was still some water left. 3 samples, 1 of them quantitative. 6. Niezgoda, the same vast alder wood com plex as on the previous locality, to the left of the road from Milicz to Żmigród. Exceptional drought lim ited the sam pling only to the deepest hollows w ith some water. 3 samples, 1 of them quantitative. 7. Olszowa Droga, commune Goniądz, Łomża province. The alder wood is a part of a vast com plex w ith typical vegetation and structure. 1 quantitative sample. 8. Gugny, commune Trzcianne, Łomża province. Alder wood eastwards from the road between Gugny and Strękowa Góra. Vast alder wood w ith typical vegetation and structure. 1 quantitative sample. http://rcin.org.pl Freshwater Gastrotricha of Poland. V G. Kisielewska, J. Kisielewski 16. Mrozy, Siedlce province, alder wood near railway station, small, usually rather dry w ith a not very typical structure and vegetation. 2 qualitative samples. 17. Kołbiel surroundings, Siedlce province, NE from the road crossing from Góra Kalwaria to Mińsk Mazowiecki and W arsaw-Lublin. Small alder wood w ith ty p ica l v eg e tation, surroudcd by meadows. 1 qualitative sample, afterwards aquarium culture. 18. W ólka W ytycka, commune Urszulin, Chełm province. Alder wood w ith a t y pical spatial structure, usually w et, on one side meadows, on the other -Sphagnum bog. 2 qualitative samples. 19. W ytyczno, commune Urszulin, Chełm province. Alder wood having a typical structure. 4 qualitative samples.