Onychopoda
| Onychopoda | ||||||||||
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Evadne spinifera |
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Onychopoda | ||||||||||
| Sars , 1865 |
The Onychopoda represent an order or subordination of the claw tails (Onychura) and thus within the leaf crabs (Branchiopoda). These are predatory small crabs that can be found in fresh water as well as in the sea. While the seawater forms occur worldwide, the freshwater forms are limited to the northern hemisphere ( Holarctic ) with a particularly high species density in the area of the Caspian Sea .
Construction of the Onychopoda
The Onychopoda reach a maximum body length of about 12 millimeters, with the rather long tail appendage making up a large part of this body length. Most species, however, only reach a body length of around 2 millimeters. The head and thorax are relatively short and stocky, the abdomen can also be short and undivided. In many species, however, it is stretched and turns into a long tail appendage (caudal appendix) with a tail fork ( furca ). The carapace, which is actually typical for the clawed tails, forms in the Onychopoda, similar to the glass crayfish ( Leptodora kindtii ), only one brood pouch, which is, however, much more pronounced than in the latter species.
The 1st antenna is short and tubular, the 2nd antennae are large two-branched swimming legs with swimming bristles. The 1st maxilla is clearly regressed, the 2nd maxilla is completely absent. The trunk is designed so that the four pairs of thoracic legs protrude forward. These grasping legs can be used to grab prey and lead it to the mouthparts . At the front end of the head lies a single, very large compound eye .
Reproduction and development
The reproduction of the Onychopoda is predominantly parthenogenetic , with the young developing in the female's brood sac. In the course of the annual cycle there is also sexual reproduction, with which usually only two yolk-rich permanent eggs are created, which are freely released into the water. In contrast, the parthenogenetically created eggs are small and have little yolk ; they are mainly supplied by a nutrient fluid from a special tissue in the brood sac.
Systematics of the Onychopoda
The Onychopoda used to be combined with the Haplopoda (the only representative is the glass crab ), the Ctenopoda and the Anomopoda as water fleas (Cladocera), but this group probably does not represent a natural unit. The actual assignment in the system of the claw tails is controversial.
The Central European representatives belong entirely to the Polyphemidae family and can be divided into several genera :
- Evadne ; marine species, for example Evadne nordmanni
- Podon
- Pleopis ; formerly one of the Podon species, such as Pleopis polyphemoides
- Polyphemus , only native to Polyphemus pediculus
- Bythotrephes ; including Bytothrephes longmanus
literature
- Ax P (1999): "The system of the Metazoa II. A textbook of phylogenetic systematics"; Gustav Fischer Verlag.
- Gruner HE (1993): "Class Crustacea"; in Gruner HE (Ed.): "Textbook of Special Zoology, Volume I, Part 4: Arthropoda (without Insecta)"; Gustav Fischer Verlag
- Schminke HK (1997): "Crustacea, Krebse"; in Westheide, Rieger (Ed.): "Special Zoology Part 1: Protozoa and Invertebrates"; Gustav Fischer Verlag