Iceland has high availability of freshwater, and it is rich in brackish and coastal aquatic bodies. However, knowledge on rotifers and meiobenthic and planktonic crustaceans inhabiting these habitats is lacking, and the inland aquatic fauna in Iceland is relatively understudied in comparison with the fauna of adjacent marine ecosystems. The majority of past research focused on larger lakes with the exception of one study on rotifers from the 1950s (Bartoš 1951) and two more recent studies on crustacean fauna of shallow freshwater bodies (Novichkova et al. 2014, Scher et al. 2000). Data are particularly scarce for the south-western part of the country.<br> We studied the composition of selected invertebrate taxa in various aquatic (marine, brackish and freshwater) habitats from South-western Iceland with a focus on Rotifera, Cladocera and Copepoda. Samples were collected from 12 localities, including marine interstitial, freshwater temporary shallow pools, swamps, wet mosses, springs, and lakes (both brackish and freshwater). We found 39 taxa in total. Rotifera dominated the sampled water bodies, followed by Copepoda and Cladocera. Three of the recorded taxa are new for Iceland, of which two are rotifers [Trichocerca cf. mucosa (Stokes, 1896) and T. vernalis (Hauer, 1936)], and one is a marine copepod (Cyclopina gracilis Claus, 1862). For some of the sampled localities (Sikið and Leirvogsvatn Lakes, and some of the smaller habitats) we present the first data on their microinvertebrate fauna.
