Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century.

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At the end of 2002, the number of marine halacarid species was 1018, that of genera 51. A single genus, Copidognathus contains 33% of all species (336). Eleven genera are monotypic. Geographical provinces with a large number of species are the tropical western Pacific, temperate northeastern Atlantic, temperate southeastern Pacific, and Mediterranean-Black Sea. Most records of halacarid species are from temperate and tropical areas; 10% of species are known from polar zones. On a generic level, 29 genera are recorded from tropical and temperate but not from polar provinces, five genera are restricted to the tropics, and none to polar regions. The majority (920 species or 90%) of all species live in the upper 200 m. Records of genera with exclusively algivorous or brackish/fresh water species are bound to littoral habitats; all the other genera occur in more than one depth zone. Arenicolous genera, though most abundant in the littoral zone, have representatives in the bathyal. Four marine genera (Copidognathus, Halacarellus, Isobactrus, Lohmannella) have representatives in coastal fresh water, and three genera, Acarothrix, Caspihalacarus and Peregrinacarus, are predominantly inhabitants of diluted brackish and fresh water. None of the free-living halacarid genera of the world's oceans appears to be endemic to one geographical province.

At the end of 2007, the family Halacaridae, superfamily Halacaroidea, included 1118 valid species in 63 genera. The genera and the number of species (in parentheses) are: Acanthohalacarus (1), Acanthopalpus (2), Acarochelopodia (8), Acaromantis (11), Acarothrix (5), Actacarus (24), Agaue (42), Agauides (2), Agauopsis (85), Anomalohalacarus (19), Arenihalacarus (1), Arhodeoporus (31), Astacopsiphagus (1), Atelopsalis (7), Australacarus (5), Bathyhalacarus (12), Bradyagaue (17), Camactognathus (3), Caspihalacarus (1), Coloboceras (3), Colobocerasides (2), Copidognathides (3), Copidognathus (359), Corallihalacarus (1), Enterohalacarus (1), Halacarellus (47), Halacaroides (2), Halacaropsis (5), Halacarus (75), Halixodes (3), Hamohalacarus (1), Himejacarus (1), Isobactrus (26), Limnohalacarus (13), Lobohalacarus (6), Lohmannella (36), Metarhombognathus (2), Mictognathus (3), Parasoldanellonyx (3), Parhalixodes (2), Pelacarus (1), Peregrinacarus (2), Phacacarus (1), Porohalacarus (2), Porolohmannella (1), Rhombognathides (6), Rhombognathus (103), Ropohalacarus (1), Scaptognathides (11), Scaptognathus (30), Simognathus (45), Soldanellonyx (9), Spongihalacarus (1), Stygohalacarus (1), Thalassacarus (1), Thalassarachna (14), Thalassophthirius (1), Troglohalacarus (1), Tropihalacarus (2), Werthella (10), Werthelloides (1), Winlundia (2), and Xenohalacarus (1). More than 1000 species live in marine and brackish water and almost 60 species exclusively in fresh or oligohaline to mesohaline brackish water (< S18‰). The checklist presents names used for halacarid genera and species of the world, names recognized as valid, synonyms, nomina nuda, names of species inquirendae and species erroneously attributed to the family Halacaridae. All valid species are supplemented with distributional data, namely, biogeographical provinces, depth zones and habitats, and references of descriptions of genera and species.

Halacaridae (Acari) from the Atlantic coast of boreal North America. Ecological and zoogeographical analysis. 38 halacarid species from the coasts of the boreal West Atlantic Ocean have been recorded. In a wide-spread net of stations, samples were taken from different substrata in marine and brackish waters in order to obtain information on the biology and ecology of halacarid species. Several habitats with their flora, fauna and halacarid species are described. In intertidal areas on the coasts of boreal North America fewer species were found than known from European coasts. Similar habitats on the west and east coasts of the North Atlantic Ocean are compared with respect to their halacarid population. In the rhombognathine and the genus Halacarellus, most species found in the West Atlantic Ocean are known in the East Atlantic too, living in similar habitats.The genera Anomalohalacarus and Copidognathus are common both in North American and European waters, but comparable biotopes are inhabited by different species, though often related or very similar in their appearance. 45 % of the halacarid species found in the boreal West Atlantic Ocean are also known in the East Atlantic. Hypotheses as to the dispersal and geographical distributior~ of halacarid genera and species are discussed. It is supposed, that many of the amphiatlantic species invaded biotopes on the American and European coasts, shortly after these continental plates drifted apart. EINLEITUNG