Clasper
{{Short description|Male anatomical structure found in some groups of animals, used in mating}}{{redir|Valva}}
{{for|the mathematics topic|Clasper (mathematics)}}
File:Wobbegong claspers.jpg shark (Orectolobus maculatus)]]
File:Carcharhinus brevipinna JNC3077 Male parts.JPG (Carcharhinus brevipinna)]]
File:Ischyodus quenstedti or egertoni.png, showing the presence of a cephalic clasper on the head of males (as well as a pelvic clasper) but absent in females ]]
In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating.
File:Spotted Ratfish Clasper.png clasper (Hydrolagus collie). Note the many small tooth-like projections covering the exterior surface.]]
File:Harpagofututor volsellorhinus.png an extinct chimaera-relative in which males (below) had clasper structures on their heads]]
Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's cloaca during mating. The act of mating in some fish including sharks usually includes one of the claspers raised to allow water into the siphon through a specific orifice. The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position. The siphon then begins to contract, expelling water and sperm.{{cite web |url=http://www.fishbase.org/Glossary/Glossary.php?q=clasper&language=english&sc=is |title=System glossary |work=FishBase |access-date=2013-02-15}}{{cite book |title=The Timetree of Life: Cartilaginous Fishes (Chondrichthyes) |last1=Heinicke |first1=Matthew P. |last2=Naylor |first2=Gavin J. P. |last3=Hedges |first3=S. Blair |year=2009 |publisher=Oxford University Press |isbn=978-0191560156 |page=320 |url=https://books.google.com/books?id=9rt1c1hl49MC&q=Manta+birostris+fossil&pg=PA320 }} The claspers of many shark species have spines or hooks,{{Cite book|last1=Compagno|first1=Leonard J. V.|url=https://books.google.com/books?id=cxxSN4YA2i8C&q=clasper+OR+claspers|title=Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date|last2=Nations|first2=Food and Agriculture Organization of the United|date=2001|publisher=Food & Agriculture Org.|isbn=978-92-5-104543-5|language=en}} which may hold them in place during copulation.{{Cite book|last1=Klimley|first1=A. Peter|url=https://books.google.com/books?id=2My8M5tL-KIC&q=clasper|title=Great White Sharks: The Biology of Carcharodon carcharias|last2=Ainley|first2=David G.|date=1998-04-03|publisher=Academic Press|isbn=978-0-08-053260-8|language=en}} Many male holocephalans, including living chimaeras, have cephalic claspers (tenacula) on their heads, which are thought to aid in holding the female during mating.{{Cite book |last=Stahl |first=Barbara |title=Handbook of Paleoichthyology Volume 4 • Chondrichthyes III • Holocephali |date=1999 |pages=29-30}}
In entomology, it is a structure in male insects that is used to hold the female during copulation (see Lepidoptera genitalia for more).