The family Hydrozetidae occurs worldwide except in Antarctica. All species of Hydrozetidae are truly aquatic and some of them are also parthenogenetic.

Worldwide the family includes only one genus, Hydrozetes, with 36 species and three subspecies (excluding fossils) (Subías 2023). In Norway three species of Hydrozetes have so far (as of 2023) been reported, and one of them, Hydrozetes lacustris, is described here. The oldest oribatid mite that could be identified to genus, was a Hydrozetes fossil found in a deposit of Early Jurassic age (Sivhed and Wallwork 1978).


The adults are of medium size (400–700 µm long). They are brown with oval shape and have rather long legs. The notogaster lacks pteromorphs, that are wing-like structures, and has 13 or 15–17 pairs of notogastral setae. In front of the notogaster there is an elevated circular and strongly convex structure, called the lenticults (Len), which serves like an eye (Norton and Behan-Pelletier 2009).

Habitat and ecology

All species of Hydrozetidae are truly aquatic, which means that they reproduce in water, and all stages of their life cycle live in water or at its margins (Schatz and Behan-Pelletier 2008). Some species are restricted to oligotrophic, acidic waters found in peatlands; other species prefer eutrophic waters. Some species are parthenogenetic, that is, only females are present, and they are produced from unfertilized eggs, while others are bisexual (Seniczak 2011).


Norton RA and Behan-Pelletier VM (2009). Suborder Oribatida. In: GW Krantz and DE Walter (eds.). A manual of Acarology, 3rd ed. Texas Tech. University Press Lubbock, 430–564.

Schatz H and Behan-Pelletier V (2007). Global diversity of oribatids (Oribatida: Acari: Arachnida). In: Balian EV, Lévêque C, Segers H and Martens K (eds). Freshwater Animal Diversity Assessment. Developments in Hydrobiology, vol 198. Springer, Dordrecht.

Seniczak A (2011). Mites (Acari) of the Shores of Forest Lakes and Ponds in Northern Poland, With Species Analysis of Oribatida. Wydawnictwa UTP, Bydgoszcz. pp. 231.

Sivhed U and Wallwork JA (1978). An Early Jurassic oribatid mite from southern Sweden. Geologiska Föreningens i Stockholm Förhandlingar, 100, 65–70.

Subías LS (2023). Listado sistemático, sinonímico y biogeográfico de los Ácaros Oribátidos (Acariformes, Oribatida) del mundo (1758−2002). Graellsia 2004, 60 (número extraordinario), 3−305. Updated 2023 – 18 actualization, 540 pp., accessed December, 2023.