Eucladocera (no evidence for grouping together all other cladocerans as the sister taxon to the monotypic Haplopoda (Leptodora))
TheDiplostraca orCladocera, commonly known aswater fleas, is asuperorder of small, mostly freshwatercrustaceans, most of which feed on microscopic chunks of organic matter, though some forms are predatory.[2]
Over 1000 species have been recognised so far, with many moreundescribed.[2][3][4][5][6] The oldest fossils of diplostracans date to theJurassic, though their modern morphology suggests that they originated substantially earlier, during thePaleozoic. Some have also adapted to a life in the ocean, the only members of Branchiopoda to do so, though severalanostracans live inhypersaline lakes.[7] Most are 0.2–6.0 mm (0.01–0.24 in) long, with a down-turned head with a single mediancompound eye, and acarapace covering the apparently unsegmentedthorax and abdomen. Most species show cyclicalparthenogenesis, whereasexual reproduction is occasionally supplemented bysexual reproduction, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.
Leptodora kindtii is an unusually large diplostracan, at up to 18 mm long.
They are mostly 0.2–6.0 mm (0.01–0.24 in) long, with the exception ofLeptodora, which can be up to 18 mm (0.71 in) long.[8] The body is not obviously segmented and bears a foldedcarapace which covers thethorax andabdomen.[9]
The head is angled downwards, and may be separated from the rest of the body by a "cervical sinus" or notch.[9] It bears a single black compound eye, located on the animal's midline, in all but two genera, and often, a singleocellus is present.[10] The head also bears two pairs ofantennae – the first antennae are small, unsegmented appendages, while the second antennae are large, segmented, and branched, with powerful muscles.[9] The first antennae bear olfactorysetae, while the second are used for swimming by most species.[10] The pattern of setae on the second antennae is useful for identification.[9] The part of the head which projects in front of the first antennae is known as therostrum or "beak".[9]
Themouthparts are small, and consist of an unpaired labrum, a pair of mandibles, a pair of maxillae, and an unpaired labium.[9] They are used to eat "organic detritus of all kinds" andbacteria.[9]
The thorax bears five or six pairs of lobed, leaf-like appendages, each with numerous hairs or setae.[9]Carbon dioxide is lost, andoxygen taken up, through the body surface.[9]
With the exception of a few purely asexual species, thelifecycle of diplostracans is dominated by asexual reproduction, with occasional periods of sexual reproduction; this is known ascyclical parthenogenesis.[11] When conditions are favourable, reproduction occurs by parthenogenesis for several generations, producing only femaleclones. As the conditions deteriorate, males are produced, and sexual reproduction occurs. This results in the production of long-lasting dormanteggs. Theseephippial eggs can be transported over land by wind, and hatch when they reach favourable conditions, allowing many species to have very wide – evencosmopolitan –distributions.[9] Except for the genus Leptodora, which has ametanauplius stage, anauplius larval stage is absent in Diplostraca.[12]
Diplostraca are nested within theclam shrimp, being most closely related to the order Cyclestherida, the only living genus of which isCyclestheria. Though several fossils from thePaleozoic have been claimed to represent fossils of diplostracans, none of these records can be confirmed. The oldest confirmed records of diplostracans are from the EarlyJurassic of Asia. Fossils from the Jurassic are assignable to modern as well as extinct groups, indicating that the initial radiation of the group occurred prior to the beginning of the Jurassic, likely during the latePaleozoic.[13] A Devonian to Carboniferous genus,Ebullitiocaris, is tentatively placed as a diplostracan, however since it is only known from carapaces this is uncertain.[1]
Most diplostracan species live infresh water and other inland water bodies, with only eight species being trulyoceanic.[10] The marine species are all in the familyPodonidae, except for the genusPenilia.[10] Some diplostracans inhabitleaf litter.[14]
According to the World Registry of Marine Species, Cladocera is a synonym of the superorder Diplostraca, which is included in the classBranchiopoda. Both names are currently in use. The superorder forms amonophyletic group of 7 orders, about 24 families, and more than 11,000 species. Many more speciesremain undescribed.[2][8] The genusDaphnia alone contains around 150 species.[11] Many groups of the water fleas are cryptic species or species flocks.[15]
Ephippia (singular: ephippium) are winter or dry-season eggs of the various species of small crustacean in the order Cladocera (within the Branchiopoda); they are provided with an extra shell layer, which preserves and protects the resting stages inside from harsh environmental conditions until the more favorable times, such as spring, when the reproductive cycle is able to take place once again. Ephippia are part of the back of a mother carrying them until they are fully developed. After molting, the ephippium stays in the water, or in the soil of dried puddles, small ponds, and vernal pools. The resting stages are often called eggs, but are in fact embryos with arrested development. Ephippia can rest for many years before the embryo resumes development upon an appropriate hatching stimulus.
^abAnderson, Lyall I.; Crighton, William R. B.; Hass, Hagen (December 2003). "A new univalve crustacean from the Early Devonian Rhynie chert hot-spring complex".Transactions of the Royal Society of Edinburgh: Earth Sciences.94 (4):355–369.doi:10.1017/S0263593300000742.
^Kotov, Alexey A.; Garibian, Petr G.; Bekker, Eugeniya I.; Taylor, Derek J.; Karabanov, Dmitry P. (2020-06-17). "A new species group from theDaphnia curvirostris species complex (Cladocera: Anomopoda) from the eastern Palaearctic: taxonomy, phylogeny and phylogeography".Zoological Journal of the Linnean Society.191 (3):772–822.doi:10.1093/zoolinnean/zlaa046.ISSN0024-4082.
^K. Van Damme; R. J. Shiel; H. J. Dumont (2007). "Notothrix halsei gen. n., sp. n., representative of a new family of freshwater cladocerans (Branchiopoda, Anomopoda) from SW Australia, with a discussion of ancestral traits and a preliminary molecular phylogeny of the order".Zoologica Scripta.36 (5):465–487.doi:10.1111/j.1463-6409.2007.00292.x.S2CID83893469.
Brusca, R.C.; Brusca, G.J. (1990). Invertebrates. Sinauer Associates: Sunderland, MA (USA). ISBN 0-87893-098-1. 922 pp
Martin, J.W., & Davis, G.E. (2001). An updated classification of the recent Crustacea. Science Series, 39. Natural History Museum of Los Angeles County. Los Angeles, CA (USA). 124 pp.
Norambuena, J., J. Farías & P. De los Ríos. (2019). he water fleaDaphnia pulex (Cladocera, Daphniidae), a possible model organism to evaluate aspects of freshwater ecosystems. Crustaceana, (11-12): 1415-1426.
Media related toDiplostraca at Wikimedia Commons
Data related toDiplostraca at Wikispecies
