Great water flea ( Daphnia magna )
|GO Sars , 1865|
The Anomopoda are a subordination of the water fleas and claw tails (Onychura). It comprises around 300 species that are found exclusively in inland waters worldwide. Above all, the anomopods living in plankton are of great ecological importance as consumers of algae and a food source for fish.
Anomopoda are relatively short and reach sizes from 0.26 mm to 6 mm. They consist of a head, a thorax with five or six pairs of legs and an abdomen without attachments. The telson is bent forward so that its dorsal side is anterior. It is used for digging as well as for pushing while crawling. Terminal it wears a pair of claws with which excess food can be removed from the feed channel.
The short head is usually equipped with a head shield, the entire rest of the body and the extremities are covered by an uncalcified carapace . This is functionally two-sided, but has no hinge. The ventral edges of the carapace can be modified in many ways, for example to ensure a balance or, in the case of a benthic way of life , to allow food to be taken in.
While the first antennae are rather small and one-piece, the second antennae are large and two-branched, so divided into endo- and exopodite. The latter has three to four segments, the endopodit three. The second antennae are the primary locomotion organ of the Anomopoda and are equipped with swimming bristles. In benthic species they can also be used for digging, crawling and climbing. The first maxillae have few spines, the second maxillae are absent or are only rudimentary.
The five to six pairs of legs are built very differently, as they serve different functions. The first pair of legs can support crawling over a substrate, or, like the second and third pair of legs, stir up or scrape off food particles, and serve to further manipulate the food. The fourth and fifth pair of legs with their filter grids form the side walls of the median lane between the leg links, into which the food particles are sucked. Their exopodites generate the water flow required for this. They also help the food to be transported forward through the feed trough. The legs of the sixth pair are mostly only flap-like appendages and form the caudal end of the alley between the legs.
The complex eye emerged from a pair of systems, but has fused to form a sessile, movable individual eye . In addition, there is usually a nauplius eye . The intestinal canal can be stretched or very tortuous. The pair of maxillary nephridia serve as excretion organs. The short heart has a pair of ostia and appears barrel-shaped, with no vessels.
The paired gonads extend laterally from the intestine. The oviducts flow into the so-called brood chamber between the shell and the back of the trunk. Males are usually smaller than females. The first antennae and the first pair of legs of the males are modified to hold the females in place during reproduction.
The Anomopoda can reproduce in one or two sexes. Either yolk-rich eggs are released into the dorsal brood chamber in diploid parthenogenesis , or reproduction is bisexual, with fertilized eggs turning into so-called permanent eggs. Small, ready-made water fleas hatch after days or after the winter. Obligatory parthenogenesis can occur, but mostly bisexual and parthenogenetic generations alternate ( heterogony ).
Anomopoda occur worldwide and are restricted to inland waters. There they can occur in all habitats, i.e. in the benthal, phytal , pelagial and interstidial . Anomopoda can also be found in damp moss or in the fall foliage of rainforests. Some species also live in inland salt water. The species diversity of the Anomopoda is greater in the benthos than in the pelagic, since the possibilities for niches are greater.
Plankler among the Anomopoda, like copepods, are of great ecological importance in marine habitats, because they are the central link in the food chain between Seston and Nekton . As primary consumers, they regulate the biomass of phytoplankton and bacterial populations. Both Plankler and the anomopods of benthos are important food components of fish.
The Anomopoda comprise the following six families:
- Bosminidae Baird, 1845
- Chydoridae Stebbing, 1902
- Daphniidae Straus, 1820
- Ilyocryptidae Smirnov, 1971
- Macrothricidae Norman & Brady, 1867
- Moinidae Goulden, 1968
- Wilfried Westheide, Gunde Rieger (ed.): Special zoology. Part 1: Protozoa and invertebrates . 3. Edition. Springer-Verlag, Berlin Heidelberg 2013, ISBN 978-3-642-34695-8 , pp. 578-582 .
- G. Boxshall, A. Kotov: Anomopoda. World Register of Marine Species (WoRMS), 2013, accessed February 14, 2014 .