The term psammon is nowadays mainly used to characterize freshwater sandy beach habitats, although it was originally defined as 'a transitional zone between aquatic and soil habitats' (Schmid-Araya, 1998), and is also applicable to brackish and marine beach habitats, where the intertidal zone can be considered as psammon habitat if the sediment consists of sand and is regularly exposed (e.g.
Psammon communities have received very little attention compared to lower littoral and sublittoral meiobenthos, and psammon has been rarely treated as a single entity.
In each sampling site, samples of psammon were collected along transects across the waterline (up to 50 cm from the waterline in both directions).
A total of 156 non-overlapping taxa belonging to 12 phyla were found in the Estonian psammon communities, 69 taxa occurring in the Gulf of Finland and 123 taxa in lakes (Table 2).
According to the present information on global distribution of rotifers (Segers, 2007; Jersabek and Leitner, 2013), of the rotifer species recorded in the psammon of the studied water bodies, 48 (58%) are cosmopolitan and other 22 (27%) have a wide distribution covering both Palaearctic and Nearctic, several of these are also known from some other biogeographic regions.
Testate amoebae are another key component of psammon, although much less information is available about this highly diverse group.