# Clam shrimp

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Orders of aquatic crustaceans sharing a common name

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Clam shrimp Temporal range: Devonian–Recent PreꞒ Ꞓ O S D C P T J K Pg N California clam shrimp, Cyzicus californicus Scientific classification Kingdom: Animalia Phylum: Arthropoda Clade: Pancrustacea Class: Branchiopoda Subclass: Phyllopoda Superorder: Diplostraca Groups included Cyclestherida Sars, 1899 Laevicaudata Linder, 1945 Spinicaudata Linder, 1945 Cladistically included but traditionally excluded taxa Anomopoda G.O. Sars, 1865 Ctenopoda G.O. Sars, 1865 Haplopoda G.O. Sars, 1865 Onychopoda G.O. Sars, 1865

**Clam shrimp** are a group of [branchiopod](/source/Branchiopod) [crustaceans](/source/Crustacean) that possess bivalved [carapaces](/source/Carapace), which resemble the [shells](/source/Seashell) of unrelated [bivalved molluscs](/source/Bivalvia).[1] They were traditionally classified in the [order](/source/Order_(biology)) **Conchostraca**, but this group later proved to be [paraphyletic](/source/Paraphyletic), because [Diplostraca](/source/Diplostraca), the water fleas, are nested within the [clade](/source/Clade) of clam shrimps; this implies certain groups of water fleas are closer to certain groups of clam shrimp than either are to other Diplostracan groups which they may resemble.[2] Clam shrimp are now divided into three orders, **Cyclestherida**, **Laevicaudata**, and **Spinicaudata**, in addition to the fossil family [Leaiidae](https://en.wikipedia.org/w/index.php?title=Leaiidae&action=edit&redlink=1).[3][4] Their fossil record is known from at least the [Devonian period](/source/Devonian_period) and perhaps before.[5]

## Characteristics

This is missing information about the diagnostic characters of the orders. Please expand the to include this information. Further details may exist on the talk page. (September 2025)

Both valves of the shell are held together by a strong closing [muscle](/source/Muscle). The animals react to danger by contracting the muscle, so that the valves close tightly and the crustacean, as if dead, lies motionlessly at the bottom of the pool.

In most species the head is [dorsoventrally](/source/Anatomical_terms_of_location#Dorsal_and_ventral) compressed. The [sessile](/source/Sessility_(zoology)) [compound eyes](/source/Compound_eye) are close together and located on the forehead; in the genus *Cyclestheria* they are truly fused. In front of them is a simple [naupliar](/source/Nauplius_(larva)) eye. The first pair of [antennae](/source/Antenna_(biology)) is reduced and unsegmented. The second pair of antennae, however, is long and biramous. Both branches are covered with numerous bristles. The crustaceans swim primarily by swooping the antennae. In the common genus *Lynceus*, which can open its spherical valves wide, the [thoracic](/source/Thoracic) legs move in an oar-like manner along with the antennae.

The number of segments constituting the thorax varies from 10 to 32, and the number of legs varies accordingly. They are similar in structure to the legs of [tadpole shrimp](/source/Tadpole_shrimp), and similarly, their size decreases from front to back. In females, the outer lobes of several middle legs are modified into long, upward-bending threadlike outgrowths, used to hold the eggs on the dorsal side of the body under the shell. However, the main functions of the thoracic legs are respiration and carrying food forward to the mouth. The gills are basically the outer lobes of all thoracic legs that are closest to the base of the leg. The legs are in constant movement, and the water between the valves of the [carapace](/source/Carapace) is quickly renewed. The body ends in a large [chitinised](/source/Chitin) [telson](/source/Telson), which is either [laterally](/source/Anatomical_terms_of_location#Directional_terms) compressed and bears a pair of large hooks, or dorsoventrally compressed, with short hooks.

## Reproduction and development

### Reproduction

Clam shrimp have different reproductive strategies. For example, within the family [Limnadiidae](/source/Limnadiidae) are found [dioecious](/source/Dioecy) (male-female), [hermaphroditic](/source/Hermaphroditic) (only hermaphrodites), and [androdioecious](/source/Androdioecious) (male-hermaphrodite) species.

### Life cycle

The eggs are surrounded by a tough shell and can withstand [drying out](/source/Desiccation), [freezing](/source/Freezing), and other hostile conditions. In some species these eggs can hatch after as long as 7 years.

When the egg arrives in a suitable [body of water](/source/Body_of_water), such as a pool, a larva hatches out at the [nauplius](/source/Nauplius_(larva)) stage (the nauplius stage is absent in Cyclestherida).[6] Clam shrimp nauplii are distinguished by very small front [antennae](/source/Antenna_(zoology)). At the second stage ([metanauplius](/source/Metanauplius)), the larva develops the small shell. They develop very quickly. For instance, *Cyzicus* reaches sexual maturity in 19 days after hatching.

## Taxonomy

Extant clam shrimp belong to three orders, divided into five families;[7] some notable genera and [prehistoric](/source/Prehistoric) [taxa](/source/Taxa) are also listed:

Spinicaudata Linder, 1945 Cyzicidae Stebbing, 1910 Caenestheria Caenestheriella Cyzicus Eocyzicus Eosestheriidae Zhang & Chen, 1976 (fossil) Bairdestheria Menucoestheria Gallego & Covacevich, 1998 Euestheridae Defretin, 1965 (fossil) Laxitextella Kozur, 1982 Leptestheriidae Daday, 1923 Eoleptestheria Leptestheria Leptestheriella Maghrebestheria Sewellestheria Limnadiidae Baird, 1849 (including Imnadiidae) Afrolimnadia Calalimnadia Eulimnadia Imnadia Limnadia Limnadiopsis Limnadiopsidum Metalimnadia Palaeolimnadiidae Tasch, 1956 (fossil) Krasiestheria Olempska, 2004 (tentatively placed here) Cyclestherida Sars, 1899 Cyclestheriidae Sars, 1899 Cyclestheria Paracyclestheria Laevicaudata Linder, 1945 Lynceidae Baird, 1845 Leptestheriella Limnetis Lynceiopsis Lynceus Paralimnetis

### Fossil record

Modern clam shrimp have little significance to humans. However, extinct species of these crustaceans are often studied by [geologists](/source/Geologist). In [freshwater](/source/Freshwater) deposits, generally poor in fossils,[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] the well-preserved clam shrimp shells are found quite often. They help identify the age of the corresponding [strata](/source/Stratum),[8] a practice known as [biostratigraphy](/source/Biostratigraphy).

During the past geological periods clam shrimp were apparently more numerous and diverse than they are now. 300 extinct species are known, twice that of living species. The oldest clam shrimp, such as *[Asmussia murchisoniana](/source/Asmussia_murchisoniana)*, were found in [Devonian](/source/Devonian) deposits. Many extinct species, mostly Triassic specimens, once [lived in marine environments](/source/Marine_life), where no extant clam shrimp inhabit today.

## See also

- *[Isoxys](/source/Isoxys)*

## References

1. **[^](#cite_ref-Webb1979_1-0)** J. Webb (1979). "A reappraisal of the palaeoecology of conchostracans (Crustacea: Branchiopoda)". *[Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen](/source/Neues_Jahrbuch_f%C3%BCr_Geologie_und_Pal%C3%A4ontologie%2C_Abhandlungen)*. **158** (2): 259–275. [doi](/source/Doi_(identifier)):[10.1127/njgpa/158/1979/259](https://doi.org/10.1127%2Fnjgpa%2F158%2F1979%2F259).

1. **[^](#cite_ref-2)** ["Conchostraca"](https://www.marinespecies.org/aphia.php?p=taxdetails&id=148393). *WoRMS*. [World Register of Marine Species](/source/World_Register_of_Marine_Species). Retrieved 2025-09-08.

1. **[^](#cite_ref-VanDamme2016_3-0)** Van Damme, Kay; Kotov, Alexey A. (December 2016). ["The fossil record of the Cladocera (Crustacea: Branchiopoda): Evidence and hypotheses"](https://linkinghub.elsevier.com/retrieve/pii/S0012825216303701). *Earth-Science Reviews*. **163**: 162–189. [Bibcode](/source/Bibcode_(identifier)):[2016ESRv..163..162V](https://ui.adsabs.harvard.edu/abs/2016ESRv..163..162V). [doi](/source/Doi_(identifier)):[10.1016/j.earscirev.2016.10.009](https://doi.org/10.1016%2Fj.earscirev.2016.10.009).

1. **[^](#cite_ref-worms_4-0)** ["Diplostraca"](http://marinespecies.org/aphia.php?p=taxdetails&id=155670). *WoRMS, World Register of Marine Species*. Retrieved 2021-11-23.

1. **[^](#cite_ref-Woolfe1990_5-0)** K. J. Woolfe (1990). "Trace fossils as paleoenvironmental indicators in the Taylor Group (Devonian) of Antarctica". *[Palaeogeography, Palaeoclimatology, Palaeoecology](/source/Palaeogeography%2C_Palaeoclimatology%2C_Palaeoecology)*. **80** (3–4): 301–310. [Bibcode](/source/Bibcode_(identifier)):[1990PPP....80..301W](https://ui.adsabs.harvard.edu/abs/1990PPP....80..301W). [doi](/source/Doi_(identifier)):[10.1016/0031-0182(90)90139-X](https://doi.org/10.1016%2F0031-0182%2890%2990139-X).

1. **[^](#cite_ref-6)** Fritsch, M.; Richter, S. (2015). "How the cladoceran heterogonic life cycle evolved--insights from gamogenetic reproduction and direct development in Cyclestherida". *Evolution & Development*. **17** (6): 356–366. [doi](/source/Doi_(identifier)):[10.1111/ede.12163](https://doi.org/10.1111%2Fede.12163). [PMID](/source/PMID_(identifier)) [26486940](https://pubmed.ncbi.nlm.nih.gov/26486940). [S2CID](/source/S2CID_(identifier)) [1932950](https://api.semanticscholar.org/CorpusID:1932950).

1. **[^](#cite_ref-M&D_7-0)** Joel W. Martin & George E. Davis (2001). [*An Updated Classification of the Recent Crustacea*](https://web.archive.org/web/20130512091254/http://atiniui.nhm.org/pdfs/3839/3839.pdf) (PDF). [Natural History Museum of Los Angeles County](/source/Natural_History_Museum_of_Los_Angeles_County). p. 132. Archived from [the original](http://atiniui.nhm.org/pdfs/3839/3839.pdf) (PDF) on 2013-05-12. Retrieved 2011-04-04.

1. **[^](#cite_ref-8)** Scholze, Frank; Shen, Shu-Zhong; Backer, Malte; Wei, Hai-Bo; Hübner, Marcel; Cui, Ying-Ying; Feng, Zhuo; Schneider, Joerg W. (June 2020). ["Reinvestigation of conchostracans (Crustacea: Branchiopoda) from the Permian–Triassic transition in Southwest China"](https://www.sciencedirect.com/science/article/abs/pii/S1871174X18301367). *[Palaeoworld](/source/Palaeoworld)*. **29** (2): 368–390. [doi](/source/Doi_(identifier)):[10.1016/j.palwor.2019.04.007](https://doi.org/10.1016%2Fj.palwor.2019.04.007). [S2CID](/source/S2CID_(identifier)) [189973963](https://api.semanticscholar.org/CorpusID:189973963). Retrieved 15 July 2023.

## External links

- [Crustaceans portal](https://en.wikipedia.org/wiki/Portal:Crustaceans)
- [Arthropods portal](https://en.wikipedia.org/wiki/Portal:Arthropods)

- [\[1\]](http://www.sacsplash.org/critter/clam-shrimp)

- [Introduction to the Branchiopoda](http://www.ucmp.berkeley.edu/arthropoda/crustacea/branchiopoda.html)

- Data related to [Cyclestherida](https://species.wikimedia.org/wiki/Cyclestherida) at Wikispecies

- Data related to [Laevicaudata](https://species.wikimedia.org/wiki/Laevicaudata) at Wikispecies

- Data related to [Spinicaudata](https://species.wikimedia.org/wiki/Spinicaudata) at Wikispecies

v t e Families of class Branchiopoda Kingdom Animalia Phylum Arthropoda Subphylum Crustacea Anostraca Artemiidae Branchinectidae Branchipodidae Chirocephalidae Parartemiidae Streptocephalidae Tanymastigidae Thamnocephalidae Notostraca Triopsidae Triops Lepidurus Laevicaudata Lynceidae Spinicaudata Cyzicidae Leptestheriidae Limnadiidae Cyclestherida Cyclestheriidae Cladocera Ctenopoda Holopediidae Pseudopenilidae Sididae Anomopoda Bosminidae Chydoridae Daphniidae Ilyocryptidae Macrotrichidae Moinidae Onychopoda Cercopagididae Podonidae Polyphemidae Haplopoda Leptodoridae

Taxon identifiers Conchostraca Wikidata: Q22111101 Wikispecies: Conchostraca ITIS: 83768 Paleobiology Database: 133417 WoRMS: 148393 Cyclestherida Wikidata: Q21217579 Wikispecies: Cyclestherida AFD: Cyclestherida ITIS: 609951 NCBI: 116559 Open Tree of Life: 1068606 Laevicaudata Wikidata: Q500917 Wikispecies: Laevicaudata AFD: Laevicaudata BugGuide: 391509 Fauna Europaea: 14764 Fauna Europaea (new): 8c1d554a-2f21-4d48-830e-4d5717500bb5 ITIS: 609949 NCBI: 116558 WoRMS: 593143 Spinicaudata Wikidata: Q1475440 Wikispecies: Spinicaudata AFD: Spinicaudata BugGuide: 1154023 Fauna Europaea: 13258 Fauna Europaea (new): 37897807-46ca-4c7c-a51d-db4589c3db1d ITIS: 609950 NCBI: 77657 NZOR: 3394b38e-570c-434e-a4dd-cf44b69e434b Paleobiology Database: 57393 WoRMS: 367238

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Adapted from the Wikipedia article [Clam shrimp](https://en.wikipedia.org/wiki/Clam_shrimp) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Clam_shrimp?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.