Sea mites
| Sea mites | ||||||||||||
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Copidognathus fabricii |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Halacaridae | ||||||||||||
| Murray , 1877 |
The marine mites (Halacaridae) are about 1,100 kinds comprehensive family mostly living in the sea mites .
features
Sea mites reach a body size of 150 micrometers to a maximum of two millimeters. Of the four pairs of legs, the front two are directed forward and the rear two are directed backward. The body is relatively weakly sclerotized; on the back (dorsal) side of the trunk (idiosoma) it has four more heavily sclerotized plates that can rarely be fused or reduced. Three small eyes can sit dorsally. The relatively short legs have six segments, named trochanter, basifemur, telofemur, genu, tibia and tarsus, with two claws at the end. The buttons (palps) have four segments. Sea mites do not have open spiracles. The gnathosoma has a protrusion (rostrum), the chelicerae sitting on it are elongated (sometimes stiletto-shaped) directed forward, they serve as piercing mouthparts with which the food is pierced. Often the first pair of legs is enlarged and used to hold food. The animals only consume liquid food, which is presumably pre-digested by secreted enzymes.
Life cycle
The species are separate sexes, only a single parthenogenetic species is known ( Isobactrus setosus (Lohmann, 1889)). For fertilization, the male releases a spermatophore . The female deposits the fertilized eggs one by one in the habitat, usually in crevices or bored into the substrate, with some genera there are also small clutches. Species living in the sand gap system often have several eggs of very different sizes, with the large ones having a complicated surface structure. A larva with six legs hatches from the egg of the sea mite, followed by one to three, but mostly two nymph stages with eight legs, the last of which sheds its skin to become an adult . The number of eggs laid by a female is relatively small, almost always less than 50. The development time is usually one year. The lifespan of the adult animals usually ranges from five to nine months. The nymphs and larvae live in the same habitat as the adults with a similar way of life.
ecology
The way of life in the sea is a peculiarity of the Halacaridae, besides this family only very few other marine mite species are known, which mostly only occur in the beach area. The group goes back to land-living ancestors who immigrated (or returned) to the sea secondarily. A variety of diets and lifestyles are realized within the halacarid family. However, all species live on the ground (“benthic”) and cannot swim. Due to their small size, they are counted among the so-called meiofauna , i. H. they are larger than the microfauna (especially protozoa), but smaller than the macrofauna (e.g. polychaete annelid worms , echinoderms, mussels). Their proportion of individuals in the meiofauna is usually relatively small, but they are very widespread and almost always at least individually involved in corresponding samples. Sea mites live in all marine habitats, from polar to tropical latitudes and from the splash zone of the beach to deep-sea trenches 7000 meters deep. Sea mites often live in the gap system of coarse-grained marine sediments (“interstitial” or “ mesopsammon ”). They belong to the so-called sand gap fauna here . Species of this family of mites can also be found on the soil surface between the flaky organic sediment. Other species live on algae or (“epizoic”) on larger marine animals such as sponges , barnacles , mussels, polychete worms or echinoderms . In some species a parasitic way of life has been demonstrated or is suspected. One species lives in the intestines of starfish, others between the gills of crabs and mollusks.
Most species presumably live on bacteria and fungi, e.g. B. the species-richest genus Copidognathus , which with 366 species alone makes up a third of the number of species. Other species are predators or parasites. In a number of genera, e.g. B. Rhombognathus with 93 species, a herbivorous (phytophagous) diet has been proven unquestionably, these pierce algae threads, which they then suck out.
Sea mites are absent in areas with fine-grained, silty soil, in oxygen-free sediments and in disturbed and often relocated sediments. They are not very resistant to marine pollution. They could potentially be used as indicators of human interference.
Biogeography and Distribution
Sea mites are known from all oceans, differences in the number of species between different sea areas are probably primarily due to different recording intensities. Although there are some quite widespread species, the species are predominantly restricted to limited sea sections, there are no globally distributed species, but probably also no endemics with only sporadic distribution. Shallow shelf seas and the deep sea as well as polar and tropical seas are also home to different fauna. For some species, it appears highly likely that they have only recently been transported to new areas by ship.
Tropical and temperate marine areas are roughly equally species-rich, while polar regions are significantly fewer in species. There are 73 known species in the Southern Ocean, but only 30 in the Arctic Ocean. 85% of the known species live in shallow marine areas, but these are considerably better known than the deep sea. Species are also known from the vicinity of hydrothermal submarine chimneys (" black smokers "), but they are not particularly rich in species or common here.
25 species are currently known from the Dutch North Sea.
Systematics
The Halacaridae family comprises around 50 genera with more than a thousand species that occur exclusively in the sea. In addition, there are 56 species from 13 genera that live in freshwater, these do not grow larger than 0.5 millimeters. The freshwater forms were occasionally separated in a family Limnohalacaridae, but this has now been recognized as an artificial system. It is believed that freshwater species have independently descended from marine forms at different times since the Paleozoic . Today a subfamily Limnohalacarinae is usually recognized, but it does not include all freshwater species.
Besides the Halacaridae themselves, the superfamily of the Halacaroidea includes only one other family, the recently described Pezidae . This family of only two species lives in fresh water, exclusively in Australia.
Web links
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- Ilse Bartsch: Geographical and ecological distribution of marine halacarid genera and species (Acari: Halacaridae). In: Experimental and Applied Acarology. Vol. 34, No. 1/2, 2002, pp. 37-58, doi : 10.1023 / B: APPA.0000044438.32992.35 .
- Ilse Bartsch: Halacaroidea (Acari): a guide to marine genera. In: Organisms Diversity & Evolution. 6, Electronic Supplement 6, 2006, pp. 1–104, online (PDF; 4.01 MB) .
- Ilse Bartsch: Global diversity of halacarid mites (Halacaridae: Acari: Arachnida) in freshwater. In: Estelle V. Balian, Christian Lévêque, Hendrik Segers, Koen Martens (eds.): Freshwater Animal Diversity Assessment (= Developments in Hydrobiology. 198). Springer, Dordrecht 2008, ISBN 978-1-4020-8258-0 , pp. 317-322, doi : 10.1007 / 978-1-4020-8259-7_34 .
- Ilse Bartsch, Harry Smit: A checklist from the nederlandse zeemijten. In: Nederlandse Faunistische Mededelingen. Vol. 25, No. 8, 2006, ISSN 0169-2453 , pp. 25-32, digitized version (PDF; 129.36 kB) .