Astigmatina
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Scabies mite ( Sarcoptes scabiei ) |
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The astigmatina are a group of small mites which, depending on the systematic approach, are regarded as order or subordination (then as astigmata ), according to the mite system of GW Krantz and DE Walter as a cohort . The group is distributed worldwide and has populated almost all habitats. Many species are parasites , for example the causative agents of scabies and mange ( grave mites ( Sarcoptes ), family Sarcoptidae and sucking mites ( Psoroptes ), family Psoroptidae ).
features
They are small animals with a body length of 0.2 to 1.8 millimeters. They are fair-skinned and unarmoured except for thin shields on the back of some species. The body probably consists of 14 segments , which in most species are so completely fused that there is often no separation into prosoma and opisthosoma ( idiosoma ), whereby a seam can often still be seen between these areas. Trichobothria and mostly the eyes are missing on the front back . The back of the body is usually sac-like and has two lateral glands, often referred to as oil glands. Podocephalic ducts are present within the body . Trachea (and thus also their openings, the stigmas) are missing, and there is no heart either.
The mouthparts can be greatly modified in the case of parasitic forms, but normally comprise scissor-shaped chelicerae , which are not covered by a roof and are therefore visible from above, and small, two-part pedipalps . Rutella (jaw shop) are missing. The legs have no real claws, but can end like claws and have a pulvillus . Their coxae are included in the abdominal surface of the idiosoma, so that only their anterior and posterior borders are visible as apodemes .
The sexual dimorphism is usually pronounced. The males have an aedeagus and a pair of suction cups on the anus for attachment to the female and bristles that have been converted into adhesive structures on the tarsi of the fourth pair of legs, which often differs significantly from the other pairs of legs. The females have in addition to the oviporus (laying opening) a bursa copulatrix (mating pouch), which lies at the end of the body or on the back.
development
After the larva , there are two nymph stages (protonymph and tritonymph). In some genera, especially under unfavorable living conditions, deutonymphs also occur, which in their appearance differ greatly from the other nymphs and the adult animals, have a thicker cuticle and stunted mouthparts. They can be designed as mobile wandering nymphs, which have a number of suction cups on the belly behind the coxae, with which they can attach themselves to other animals and thus get into more suitable habitats, where they usually develop into tritonymphs. Deutonymphs can also be developed as permanent nymphs with short or completely reduced legs, which are immobile and in some species remain within the cuticle of the protonymph. These permanent stages are very resistant to drought, heat and cold and can thus ensure the survival of a local population over unfavorable months. Most species can only develop one of the two deutonymph forms.
Systematics
External system
The exact position of the astigmatina within the mites is controversial. Since the group changes rapidly in evolution , both morphological and molecular biological investigations yield results that are difficult to interpret. Classically, the astigmata were regarded as one of four large groups within the mites alongside the horn mites (Oribatida), the endostigmata and the trombidiformes . The close relationship between Astigmatina and Oribatida is widely accepted and recent molecular biological studies show that the Astigmatina probably represent a group within the Oribatida. According to this, the Astigmata as a group are around 370 million years old, with the oldest fossil evidence coming from amber that is 35 to 40 million years old .
Internal system
Within the Astigmatina, two groups with around 3000 species are distinguished in 12 superfamilies and around 70 families:
- Acaridia (primarily wild animals)
- Psoroptidia
- predominantly parasitic animals
- incertae sedis
The oldest known fossil representative of the Astigmata is the species Glaesacarus rhombeus of the extinct monotypical family Glaesacaridae, which occurs frequently in the Eocene Baltic amber .
literature
- Hans-Eckhard Gruner (Ed.): Textbook of Special Zoology, Volume I: Invertebrates, Part 4: Arthropods (without Insecta) . 4th edition. Gustav Fischer, Jena, Stuttgart, New York 1993, ISBN 3-334-60404-7 , pp. 392-394 .
- Miroslawa Dabert, Wojciech Witalinski, Andrzej Kazmierski, Ziemowit Olszanowski, Jacek Dabert: Molecular phylogeny of acariform mites (Acari, Arachnida): Strong conflict between phylogenetic signal and long-branch attraction artifacts . In: Molecular Phylogenetics and Evolution . tape 56 , 2010, p. 222-241 (English).
Individual evidence
- ↑ Astigmata in Hallan's Catalog of Biology ( Memento of the original of February 16, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
