Branchiopoda

Branchiopoda, from Ancient Greek βράγχια (bránkhia), meaning "gill", and πούς (poús), meaning "foot", is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Diplostraca (or Cladocera), Notostraca, the Devonian Lepidocaris and possibly the Cambrian Rehbachiella. They are mostly small, freshwater animals that feed on plankton and detritus.

Description

Members of the Branchiopoda are unified by the presence of gills on many of the animals' appendages, including some of the mouthparts. This is also responsible for the name of the group<ref>Template:Cite book</ref> (from the Template:Langx, gills, akin to {{#invoke:Lang|lang}}, windpipe; Template:Langx, foot).<ref>Template:Cite book</ref> 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).<ref name="Hyman">Template:Cite book</ref> In the groups where the carapace prevents the use of the trunk limbs for swimming (Cladocera and clam shrimp), the antennae are used for locomotion, as they are in the nauplius.<ref name="Hyman"/> Male fairy shrimp have an enlarged pair of antennae with which they grasp the female during mating, while in the bottom-feeding Notostraca, the antennae are reduced to vestiges.<ref name="Hyman"/> 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.<ref name="Hyman"/>

Ecology

Branchiopods are found in continental fresh water, including temporary pools and in hypersaline lakes, and some in brackish water. Only two groups of water fleas include marine species: Family Podonidae in the order Diplostraca, and family Sididae in the order Diplostraca.<ref>Template:Cite book</ref><ref>Marine Biology: A Functional Approach to the Oceans and their Organisms</ref><ref>Biology of Cladocera: Proceedings of the Second International Symposium on Cladocera</ref> Most branchiopodans eat floating detritus or plankton, which they take using the setae on their appendages.<ref name="Hyman"/> But notostracans are omnivorous and very opportunistic feeders and will eat algae and bacteria in addition to animals as both predators and scavengers.<ref>Template:Cite journal</ref>

Taxonomy

In early taxonomic treatments, the current members of the Branchiopoda were all placed in a single genus, Monoculus.<ref name="Jørgensen"/> The taxon Branchiopoda was erected by Pierre André Latreille in 1817, initially at the rank of order.<ref name=Cuvier1831/>

The current upper-level classification of Branchiopoda, according to the World Register of Marine Species (2021), is as follows:<ref name=worms/>

Class Branchiopoda Latreille, 1817

Subclass Sarsostraca Tasch, 1969

Order Anostraca Sars, 1867

Suborder Anostracina Weekers et al., 2002

Suborder Artemiina Weekers et al., 2002

Subclass Phyllopoda Preuss, 1951

Superorder Diplostraca Gerstaecker, 1866

Order Anomopoda G.O. Sars, 1865

Order Ctenopoda G.O. Sars, 1865

Order Cyclestherida Sars G.O., 1899

Order Haplopoda G.O. Sars, 1865

Order Laevicaudata Linder, 1945

Order Onychopoda G.O. Sars, 1865

Order Spinicaudata Linder, 1945

Order Notostraca G. O. Sars, 1867

Genus †Rehbachiella? Müller, 1983

In addition, the extinct genus Lepidocaris is generally placed in Branchiopoda.

Anostraca

File:Artemia salina 3.jpg

Artemia salina (Anostraca: Artemiidae)

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} The fairy shrimp of the order Anostraca are usually Template:Convert long (exceptionally up to Template:Convert).<ref name="Belk"/> Most species have 20 body segments, bearing 11 pairs of leaf-like phyllopodia (swimming legs), and the body lacks a carapace.<ref name="Khanna">Template:Cite book</ref> They live in vernal pools and hypersaline lakes across the world, including pools in deserts, in ice-covered mountain lakes and in Antarctica. They swim "upside-down" and feed by filtering organic particles from the water or by scraping algae from surfaces.<ref name="Belk"/> They are an important food for many birds and fish, and are cultured and harvested for use as fish food.<ref name="Jørgensen"/> There are 300 species spread across 8 families.<ref name="Diversity">Template:Cite journal</ref>

Lipostraca

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Lipostraca contains a single extinct Early Devonian species, Lepidocaris rhyniensis,<ref>Template:Cite book</ref> which is the most abundant animal in the Rhynie chert deposits.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It resembles modern Anostraca, to which it is probably closely related, although its relationships to other orders remain unclear.<ref>Template:Cite journal</ref> The body is Template:Convert long, with 23 body segments and 19 pairs of appendages, but no carapace.<ref>Template:Cite journal</ref> It occurred chiefly among charophytes, probably in alkaline temporary pools.<ref name="abdn">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Notostraca

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} The order Notostraca comprises the single family Triopsidae, containing the tadpole shrimp or shield shrimp.<ref name="Lowry">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The two genera, Triops and Lepidurus, are considered living fossils, having not changed significantly in outward form since the Triassic.<ref name="Diversity"/> They have a broad, flat carapace, which conceals the head and bears a single pair of compound eyes.<ref name="Belk"/> The abdomen is long, appears to be segmented and bears numerous pairs of flattened legs.<ref name="Belk"/> The telson is flanked by a pair of long, thin caudal rami.<ref name="Hyman"/> Phenotypic plasticity within taxa makes species-level identification difficult, and is further compounded by variation in the mode of reproduction.<ref name="Diversity"/><ref>Template:Cite journal</ref> The evidence of phenotypic plasticity of Arctic tadpole shrimp (Lepidurus arcticus, Notostraca) has been observed in Svalbard.<ref name=":0">Template:Cite book</ref> Notostracans are the largest branchiopodans and are omnivores living on the bottom of temporary pools, ponds<ref name=":0">Template:Cite book</ref> and shallow lakes.<ref name="Belk"/>

Laevicaudata, Spinicaudata and Cyclestherida (once Conchostraca)

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} 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.

Anomopoda, Ctenopoda, Onychopoda, and Haplopoda (once Cladocera)

File:Daphnia pulex.png

Daphnia pulex (Cladocera: Daphniidae)

These four orders make up a group of small crustaceans commonly called water fleas. Around 620 species have been recognised so far, with many more undescribed.<ref name="Forró">Template:Cite journal</ref> They are ubiquitous in inland aquatic habitats, but rare in the oceans.<ref name="Belk">Template:Cite book</ref> Most are Template:Convert long, with a down-turned head, and a carapace covering the apparently unsegmented thorax and abdomen.<ref name="Pennak_Cladocera">Template:Cite book</ref> There is a single median compound eye.<ref name="Belk"/> Most species show cyclical parthenogenesis, where asexual reproduction is occasionally supplemented by sexual reproduction, which produces resting eggs that allow the species to survive harsh conditions and disperse to distant habitats.<ref name="Decaestecker">Template:Cite book</ref> In the water bodies of the world, a lot of Cladocera are non-native species, many of which pose a great threat to aquatic ecosystems.<ref>Template:Cite journal</ref>

Evolution

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.<ref name="M&D">Template:Cite book</ref> 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.<ref name="Belk"/> Although they were previously considered the sister group to the remaining crustaceans, it is now widely accepted that crustaceans form a paraphyletic group, and Branchiopoda are thought to be sister to a clade comprising Xenocarida (Remipedia and Cephalocarida) and Hexapoda (insects and their relatives).<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

See also

• Vladicaris