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[[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 [[egg]]s of [[Oviparity|oviparous]] [[Chondrichthyes|chondrichthyans]]. Living chondricthyans that produce egg cases include some [[shark]]s, [[Skate (fish)|skate]]s and [[chimaera]]s. Egg cases typically contain one embryo, except for [[big skate]] and [[mottled skate]] egg cases, which contain up to 7 embryos.<ref name="Ebert2"/> [[Oviparity]] is completely absent in the superorder [[Squalomorphii]].<ref name=":1" /><ref name="1st ed" /> Egg cases are also thought to have been produced by some extinct chondricthyan groups, such as [[hybodonts]] and [[Xenacanthida|xenacanths]].
== 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}}</ref> and are often described as feeling rough and leathery.<ref name=":2" /> Some egg cases have a fibrous material covering the outside of the egg case, thought to aid in attachment to substrate.<ref name="Ebert2"/><ref name=":3">{{Cite journal|
== 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> Hatchlings are considered large for sharks, reaching over 14 cm in length by the time they leave the egg case.<ref name=":2" /> Bullhead shark eggs typically hatch after 7 to 12 months, depending on the species.<ref name=":2" /> The
[[File:Chiloscyllium punctatum egg sunshine international.jpg|thumb|upright=0.8|Egg case of a [[brownbanded bamboo shark]]]]
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=== 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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