(Redirected from
Cladocera)
Suborder Anomopoda
Daphniidae
Moinidae
Bosminidae
Macrothricidae
Chydoridae
Suborder Ctenopoda
Sididae
Holopedidae
Suborder Onychopoda
Polyphemidae
Cercopagidae
Podonidae
Suborder Haplopoda
Leptodoridae
Daphnia are members of the order Cladocera. They are one of the several small aquatic crustaceans called Water Fleas because they tend to swim by making little jumps.
Biology
Daphnia are small, mainly planktonic, crustaceans, between 0.2 and 5 mm in length. They live in various aquatic environments ranging from acidic swamps, lakes, ponds, streams and rivers.
The division of the body into segments is nearly invisible. The head is fused, and is generally bent down towards the body with a visible notch separating the two. In most species the rest of the body is covered by a carapace, with a ventral gap in which lie the five or six pairs of legs. The most prominent features are the compound eyes, the second antennae, and a pair of abdominal setae. In many species the carapace is tranlucent or nearly so and as a result they make excellent subjects for the microscope. Even under relatively low power, it is possible to observe the feeding mechanism working, watch immature young moving in the brood-pouch, observe the eye being moved by the cillary muscles and even watch blood corpuscles being pumped round the circulatory system by the simple heart. They are tolerant of being observed live under a cover slip and appear to suffer no harm when returned to to open water.
A few Daphnia prey on tiny crustaceans and rotifers, but most are filter feeders, ingesting mainly unicellular algae and various sorts of organic detritus including protists and bacteria. Daphnia can be kept easily on a diet of yeast. Beating of the legs produces a constant current through the carapace which brings such material into the digestive tract. The first and second pair of legs are used in the organisms' filter feeding, ensuring large unabsorbable particles are kept out while the other sets of legs create the stream of water rushing into the organism. Swimming, on the other hand, is powered mainly by the second set of antennae which are larger in size than the first set. The action of this second set of antennae is responsible for the jumping motion.
Daphnia reproduce parthenogenetically usually in the spring till the end of the summer. One or more juvenile animals are nurtured in the brood pouch inside the carapace.The newly hatched Daphnia must molt several times before they are fully grown into an adult usually after about two weeks. The young are small copies of the adult; there are no true nymphal or instar stages. The fully mature females are able to produce a new brood of young about every ten days under ideal conditions. The reproduction process continues while the environmental conditions continue to support their growth. Winter or drought conditions brings an end to the production of new female generations. At this time, the reproduction method changes. Parthenogenic males are produced, followed by mating and fertilization of the eggs. Fertilized eggs are termed winter eggs and are provided with extra shell layer called ephippium. The extra layer preserves and protects the egg inside from harsh environmental conditions until the more favourable times, such as spring, when the reproductive cycle is able to take place once again.
Males are only found at times of harsh environmental conditions, typically during portions of the year of scarce resources due to population overgrowth or winter conditions, and even then may make up considerably less than half the population, in some species being unknown entirely. They are much smaller in size than the female and they typically possess a spcialised abdominal appendage which is used to grasp a female from behind and prise open her carapace and insert a spermotheca. Their appearance is for the creation of resting or winter eggs, allowing for the survival of the population through harsh conditions.
The lifespan of a Daphnia does not exceed one year and is largely temperature dependent. For example, individual organisms can live up to 108 days at three degrees celsius while some organisms live for only 29 days at 28 degrees celsius. A clear exception to this trend is during the winter time in which harsh conditions limit the population in which females have been recorded to live for over 6 months. These females generally grow at slower rate but in the end are larger than ones under normal conditions.
Daphnia provide an important source of food for many larger aquatic organisms including juvenile fish and the immature stages of many insects including the Orthoptera- Dragonflies and Dameselflies.
Taxonomy
Order: Cladocera Latreille, 1829
- Suborder Anomopoda
- Family Daphniidae Straus 1820
- Ceriodaphnia Dana 1853
- Daphnia Müller 1785
- Daphniopsis Sars 1903
- Megafenestra Dumont & Pensaert 1983
- Simocephalus Schödler 1858
- Scapholeberis Schödler 1858
- Family Moinidae Goulden 1968
- Moina Baird 1850
- Moinodaphnia Herrick 1887
- Family Bosminidae Baird 1846
- Bosmina Baird 1846
- Bosminopsis Richard 1895
- Family Macrothricidae Norman & Brady 1867
- Acantholeberis Lilljeborg 1846
- Bunops Birge 1893
- Drepanothrix Sars 1862
- Echinisca Liévin 1848
- Grimaldina Richard 1892
- Guernella Richard 1892
- Iheringula Sars 1900
- Ilyocryptus Sars 1862
- Lathonura Lilljeborg 1853
- Macrothrix Baird 1843
- Neothrix Gurney 1927
- Ophryoxus Sars 1862
- Parophryoxus Doolittle 1909
- Pseudomoina Sars 1912
- Streblocerus Sars 1862
- Wlassisca Daday 1904
- Family Chydoridae Stebbing 1902
- Acroperus Baird 1843
- Alona Baird 1843
- Alonella Sars 1862
- Alonopsis Sars 1862
- Anchistropus Sars 1862
- Archepleuroxus Smirnov & Timms 1983
- Australochydorus Smirnov & Timms 1983
- Biapertura Smirnov 1971
- Bryospilus
- Camptocercus Baird 1843
- Celsinotum Frey 1991
- Chydorus Leach 1816
- Dadaya Sars 1901
- Disparalona Sars 1862
- Dunhevedia King 1853
- Ephemeroporus Frey 1982
- Euryalona Sars 1901
- Eurycercus Baird 1843
- Graptolebris Sars 1862
- Kurzia Dybowski & Grochowski 1894
- Leberis Smirnov 1989
- Leydigia Kurz 1875
- Monope Smirnov & Timms 1983
- Monospilus Sars 1862
- Notoalona Rajapaksa & Fernando 1987
- Oxyurella Dybowski & Grochowski 1894
- Paralona Šráhek-Hušek 1962
- Phrixura P.E. Müller 1867
- Planicirclus Frey 1991
- Pleuroxus Baird 1843
- Plurispina Frey 1991
- Pseudochydorus Fryer 1968
- Rak Smirnov & Timms 1983
- Rhynchotalona Norman 1903
- Saycia Sars 1904
- Spinalona Ciros-Perez & Elias-Gutierrez 1997
- Tretocephala Frey 1965
- Suborder: Ctenopoda
- Family Sididae Baird 1850
- Diaphanosoma Fischer 1850
- Latona Straus 1820
- Latonopsis Sars 1888
- Penilia Dana 1849
- Pseudosida Herrick 1884
- Sarsilatona Korovchinsky 1985
- Sida Straus 1820
- Family Holopedidae Sars 1865
- Suborder: Onychopoda
- Family Polyphemidae Baird 1845
- Family Cercopagidae Mordukhai-Boltovskoi 1966
- Bythotrephes Leydig 1860
- Cercopagis Sars 1897
- Family Podonidae Mordukhai-Boltovskoi 1968
- Caspievadne Behning 1941
- Cornigerius Mordukhai-Boltovskoi 1967
- Evadne Lovén 1836
- Pleopsis Dana 1852
- Podon Lilljeborg 1853
- Podonevadne Gibitz 1922
- Suborder: Haplopoda
- Family Leptodoridae Lilljeborg 1861
- Leptodora Lilljeborg 1861
External links
Last updated: 05-13-2005 02:41:04
