Halacaridae

Halacaridae

Halacaridae is a large family of tiny mites. These mites live in water. You can find them in oceans, where salt and fresh water mix, and in rivers and lakes all around the world. They are very small and live among tiny plants and animals on the bottom of these water places.

There are over 1100 different kinds of these mites known to science. This makes Halacaridae the biggest group of water-dwelling spiders and their relatives in the ocean. These mites help keep water areas healthy by breaking down tiny plants and animals.

Description and life cycle

Halacarids have four pairs of legs. The first two pairs point forward, and the last two pairs point backward. They also have four plates on their backs.

Their life cycle starts with an egg, then a larva stage, followed by 1 to 3 nymph stages, and finally the adult stage. Between each stage, there is a resting pupal stage. Eggs are placed by adult females in a surface using a special body part. Larvae have three pairs of legs and no genital plate. Nymphs have four pairs of legs and usually have a genital plate. Adults look similar to the last nymph stage but have special body parts for laying eggs or transferring sperm, depending on their gender.

Halacarids also have small mouth parts called palps, usually with four segments. Some groups have fewer segments in these parts. One subgroup, Rhombognathinae, eats algae and has a dark green or black pigment in its body from the algae it eats.

Ecology

Halacaridae mites live in many places such as sandy beaches, areas with tidal sediment, tiny spaces between grains, hydrothermal vents, mangroves, salt marshes, and even on larger animals. They stay their whole lives on surfaces like algae or sand.

Most of these mites eat other small creatures, but one group, Rhombognathinae, eats algae instead. In freshwater areas, some halacarids live on crayfish. There is also a species called Lobohalacarus weberi that eats dead nematodes and oligochaetes.

Phylogeny

Scientists have found that Halacaridae is closely related to a group called Parasitengona. Inside Halacaridae, there is a subgroup called Rhombognathinae. This subgroup has two lines that eat algae, showing that this way of eating algae happened twice in their history.

Genera

Here is a list of the groups within the Halacaridae family. Each group has a special name given by scientists:

• Acanthohalacarus Bartsch, 2001
• Acanthopalpus Makarova, 1978
• Acarochelopodia Angelier, 1954
• Acaromantis Trouessart & Neumann, 1893
• Acarothrix Bartsch, 1990
• Actacarus Schulz, 1937
• Agaue Lohmann, 1889
• Agauides Bartsch, 1988
• Agauopsis Viets, 1927
• Anomalohalacarus Newell, 1949
• Arhodeoporus Newell, 1947
• Astacopsiphagus Viets, 1931
• Bathyhalacarus Sokolov & Jankovskaja, 1968
• Bradyagaue Newell, 1971
• Camactognathus Newell, 1984
• Coloboceras Trouessart, 1889
• Colobocerasides Viets, 1950
• Copidognathides Bartsch, 1976
• Copidognathus Trouessart, 1888
• Corallihalacarus Otto, 1999
• Enterohalacarus Viets, 1938
• Halacarellus Viets, 1927
• Halacaroides Bartsch, 1981
• Halacaropsis Bartsch, 1996
• Halacarus Gosse, 1855
• Halixodes Brucker & Trouessart, 1899
• Hamohalacarus Walter, 1931
• Himejacarus Imamura, 1957
• Isobactrus Newell, 1947
• Limnohalacarus Walter, 1917
• Lobohalacarus Viets, 1939
• Lohmannella Trouessart, 1901
• Metarhombognathus
• Mictognathus Newell, 1984
• Parasoldanellonyx Viets, 1929
• Parhalixodes Laubier, 1960
• Pelacarus Bartsch, 1986
• Peregrinacarus Bartsch, 1999
• Plegadognathus Morselli, 1981
• Porohalacarus Thor, 1922
• Porolohmannella Viets, 1933
• Rhombognathides Viets, 1927
• Rhombognathus Trouessart, 1888
• Ropohalacarus Bartsch, 1989
• Scaptognathides Monniot, 1972
• Scaptognathus Trouessart, 1889
• Simognathus Trouessart, 1889
• Soldanellonyx Walter, 1917
• Spongihalacarus Otto, 2000
• Stygohalacarus Viets, 1934
• Thalassacarus Newell, 1949
• Thalassarachna Packard, 1871
• Thalassophthirius Bartsch, 1988
• Troglohalacarus Viets, 1937
• Tropihalacarus Otto & Bartsch, 1999
• Werthella Lohmann, 1907
• Werthelloides Bartsch, 1986
• Winlundia Newell, 1984
• Xenohalacarus Otto, 2000