Branchiopoda Latreille, 1817
* deWaard, J.R.; Sacherova, V.; Cristescu, M.E.A.; Remigio, E.A.; Crease, T.J.; Hebert, P.D.N. 2006: Probing the relationships of the branchiopod crustaceans. Molecular phylogenetics and evolution, 39: 491-502.
Branchiopoda is a class of crustaceans. It is the sister group to the remaining crustaceans, and comprises fairy shrimp, clam shrimp, Cladocera and Notostraca. They are mostly small, freshwater animals that feed on plankton and detritus, with the exception of the Cladocera, many of which are marine.
Members of the Branchiopoda are unified by the presence of gills on many of the animal's appendages, including some of the mouthparts. This is also responsible for the name of the group (from the Greek: branchia, gills, akin to bronchos, windpipe; Greek: pous, foot). They generally possess compound eyes and a carapace, which may be a shell of two valves enclosing the trunk (as in most Cladocera), broad and shallow (as in the Notostraca), or entirely absent (as in the Anostraca). In the groups where the carapace prevents the use of the trunk limbs for swimming (Cladocera, clam shrimp and the extinct Lipostraca), the antennae are used for locomotion, as they are in the nauplius. Male fairy shrimp have an enlarged pair of antennae with which they graps the female during mating, while the bottom-feeding Notostraca, the antennae are reduced to vestiges. The trunk limbs are beaten in a metachronal rhythm, causing a flow of water along the midline of the animal, from which it derives oxygen, food and, in the case of the Anostraca and Notostraca, movement.
Among the branchiopods, only the cladocerans are found in the sea; all the other groups are found in fresh water, including temporary pools. Most branchiopodans eat floating detritus or plankton, which they take using the setae on their appendages.
In early taxonomic treatments, the current members of the Branchiopoda were all placed in a single genus, Monoculus. The taxon Branchiopoda was erected by Pierre André Latreille in 1817, initially at the rank of order.
Despite a long geological record, the only two genera in the order Notostraca (tadpole shrimp) are still extant: Triops and Lepidurus. They include species such as Triops cancriformis, which do not appear to have changed in 220 million years, and may therefore be the oldest living animal species on earth. They have a large cephalic shield and a long tail. Their ability to survive drought as eggs has allowed notostracans to be marketed as instant pets.
Laevicaudata, Spinicaudata and Cyclestherida
Clam shrimp are bivalved animals which have lived since at least the Devonian. The three groups are not believed to form a clade. They have 10–32 trunk segments, decreasing in size from front to back, and each bears a pair of legs which also carry gills. A strong muscle can close the two halves of the shell together.
Branchiopods are considered the most primitive of the crustacean classes, and the sister group to the remaining crustaceans. The fossil record of branchiopods extends back at least into the Upper Cambrian and possibly further. The group is thought to be monophyletic, with the Anostraca having been the first group to branch off. It is thought that the group evolved in the seas, but was forced into temporary pools and hypersaline lakes by the evolution of bony fishes.
1. ^ Georges Cuvier (trans. William Benjamin Carpenter) (1851). "Crustacean Entomostraca (Müller)". The animal kingdom: arranged after its organization, forming a natural history of animals, and an introduction to comparative anatomy. W. S. Orr and co.. pp. 434–448. http://books.google.co.uk/books?id=fPvRAAAAMAAJ.
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