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{{short description|Natural collagen casing found encompassing some aquatic lifeforms' fertilized eggs}}
{{Use dmy dates|date=
[[File:Mermaidpurse.jpg|thumb|upright=1.2|right|Egg case of a [[Skate (fish)|skate]]]]
[[File:Shark egg case video, Bristol Aquarium, Nov 2014.ogv|thumb|Embryo active inside egg case.]]
An '''egg case''' or '''egg capsule''', often colloquially called a '''mermaid's purse''', is the casing that surrounds the [[
== Description ==
Egg cases are made of [[collagen]] protein strands,<ref>{{cite journal|last=Evans|first=David H.|title=The egg case of the oviparous elasmobranch, Raja Erinacea, does osmoregulate|journal=Journal of Experimental Biology|volume=92|date=June 1981|doi=10.1242/jeb.92.1.337 |url=http://jeb.biologists.org/content/jexbio/92/1/337.full.pdf
== Development ==
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==Sharks==
[[File:Heterodontus portusjacksoni egg.jpg|thumb|upright=0.8|Egg case of a [[Port Jackson shark]]]]
Oviparity in sharks can be categorized as single or retained.<ref name=":1">{{Cite book|title=Biology of Sharks: Second Edition|
Oviparous sharks are known to regularly produce unfertilized eggs when kept in captivity without males.<ref>{{Cite web|url=http://www.aquariumofpacific.org/blogs/comments/egg_id|title=Egg Identification|date=2008|website=Aquarium of the Pacific}}</ref>
===Bullhead sharks===
Bullhead shark egg cases are shaped like an [[Auger (drill)|auger]], with two spiral flanges. This allows the egg cases to become wedged in the crevices of rocky sea floors, where the eggs are protected from predators; however, some bullhead sharks deposit their eggs on sponges or seaweed.<ref>{{Cite web|url=https://www.floridamuseum.ufl.edu/fish/discover/species-profiles/heterodontus-francisci/|title=Heterodontus francisci|last=Buch|first=Robert|website=Florida Museum}}</ref><ref name=":2">{{Cite journal|last=Compagno|first=Leonard|date=2002|title=Sharks of the World|journal=FAO Species Catalogue for Fishery Purposes|volume= 2|pages=31–50}}</ref>
[[File:Chiloscyllium punctatum egg sunshine international.jpg|thumb|upright=0.8|Egg case of a [[brownbanded bamboo shark]]]]
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==Skates==
[[File:Big skate egg case.JPG|thumb|upright=0.9|Egg case of a [[big skate]]]]
The [[Skate (fish)|skate]]s (Rajidae, Arhynchobatidae, Anacanthobatidae) are the only [[Batoidea|rays]] that are [[oviparous]].<ref name="Florida Museum of Natural History">{{cite web|url=http://www.flmnh.ufl.edu/fish/education/questions/Biology.html#purse|publisher=Florida Museum of Natural History|title=Most Commonly Asked Questions}}</ref> Females lay egg cases onto the sea floor after fertilization occurs [[Uterus|in utero]]. While in utero, a protected case forms around the [[embryo]] which is called the egg case.<ref name="Ebert2">Ebert, David A., Davis, Chante D. (2007). "Descriptions of skate egg cases (Chondrichthyes: Rajiformes: Rajoidei) from the eastern North Pacific". ''Zootaxa'' 1393: 1-18.</ref><ref name="Zipcodezoo">{{cite web|website=Zipcodezoo.com|url=http://zipcodezoo.com/Animals/R/Raja_binoculata/|title=''Raja binoculata'' (Big Skate, Big Skate)|archive-url=https://web.archive.org/web/20080908085320/http://zipcodezoo.com/Animals/R/Raja_binoculata|archive-date=8 September 2008 |url-status=dead}}</ref> Studies have been done where egg cases were removed from gravid females to ensure proper identification in regard to skate species.<ref name="Ebert2"/> Egg cases have distinguishable characteristic traits that are unique to that species, thus making it a great tool for identifying a skate. The two most distinguishable features on the egg case are the keel and the absence or presence of a fibrous covering. A keel runs laterally along both sides of the outer edge of the egg case; it is a flexible structure. Keels will also run the length of the horns on some skate species. Some egg cases have broad keels (greater than 10% of the maximum egg case width) while others have narrow keels (less than 10% of the maximum egg case width).<ref name="Ebert2"/> Many egg cases are covered with a layer of fiber; some will have a fine layer while others have a thick layer.
=== Big skate ===
Big skate egg cases are larger than most other skate egg cases; typically ranging from 210 to 280 mm in length and 110 to 180 mm in width.<ref name="Ebert2"/><ref name="
Big skates are one of only two skates known to have multiple embryos inside an egg case; up to 7 embryos have been found inside a single case. But most big skate egg cases contain 3–4 embryos.<ref name="Ebert, D.A., Smith, W.D., and Cailliet, G.M. (2008)2">Ebert, D.A., Smith, W.D., and Cailliet, G.M. (2008). "Reproductive biology of two commercially exploited skates, ''Raja binoculata'' and ''R. rhina'', in the western Gulf of Alaska". ''Fisheries Research'', 94:48-57. {{doi|10.1016/j.fishres.2008.06.016}}</ref>
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==Chimaeras==
[[File:Egg case elephantfish DSF0874.jpg|thumb|upright=0.8|Egg case of a [[Cape elephantfish]]]]
All known [[Chimaera|chimaeras]] produce egg cases.<ref>{{Cite journal |last1=García-Salinas |first1=Pablo |last2=Gallego |first2=Victor |last3=Asturiano |first3=Juan F. |date=2021-07-23 |title=Reproductive Anatomy of Chondrichthyans: Notes on Specimen Handling and Sperm Extraction. II. Sharks and Chimaeras |journal=Animals |language=en |volume=11 |issue=8 |pages=2191 |doi=10.3390/ani11082191 |issn=2076-2615 |pmc=8388383 |pmid=34438648 |doi-access=free }}</ref> The egg cases of
== Extinct chondrichthyans ==
[[File:Sgff a 1907442 f0011 c.jpg|thumb|Illustration of an Early Jurassic estuarine ecosystem, with ''[[Palaeoxyris]]'' egg cases attached via tendril to ''[[Neocalamites]]'' stems, with [[hybodonts]] in the background]]
The egg case genera ''[[Palaeoxyris]]'' and ''[[Fayolia]]'', which are thought to have been produced by [[hybodonts]] and [[Xenacanth|xenacanths]] respectively, two groups of extinct shark-like cartilaginous fish more closely related to modern sharks and rays than to chimaeras, resemble those of bulldog sharks in having a spiral collarettes running around them. Both ''Palaeoxyris'' and ''Fayolia'' taper towards their ends (with the tapering being more pronounced in ''Palaeoxyris''), with one end having a tendril. Unlike modern sharks, these eggs are typically found in freshwater environments.<ref>{{Cite journal |last1=Fischer |first1=Jan |last2=Licht |first2=Martin |last3=Kriwet |first3=Jürgen |last4=Schneider |first4=Jörg W. |last5=Buchwitz |first5=Michael |last6=Bartsch |first6=Peter |date=2014-04-03 |title=Egg capsule morphology provides new information about the interrelationships of chondrichthyan fishes |url=http://www.tandfonline.com/doi/abs/10.1080/14772019.2012.762061 |journal=Journal of Systematic Palaeontology |language=en |volume=12 |issue=3 |pages=389–399 |doi=10.1080/14772019.2012.762061 |bibcode=2014JSPal..12..389F |s2cid=84827548 |issn=1477-2019}}</ref>
== Threats ==
Predation on egg cases is thought to be a major source of mortality for developing oviparous sharks, skates and chimaeras.<ref name=":4">{{Cite journal|
==References==
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[[Category:Cartilaginous fish]]
[[Category:Fish reproduction]]
[[Category:Articles containing video clips]]
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