Male and female sharks differ in that male sharks have modified pelvic fins called claspers, while female sharks do not. Furthermore, male sharks have testes, while female sharks have ovaries. Male sharks also have two muscular sacs known as siphon sacs located in their abdominal wall.
Claspers are considered to be part of a male shark's sexual organs because they are used during mating. They are an external organ used to funnel and deliver sperm to the sexual organs of the female shark. During the mating process, one of the claspers is raised to allow sea water into the siphon sacs. The sea water inside the sacs is ejected under pressure and used to inject the male shark's sperm into the reproductive organs of the female shark. The second clasper is inserted into the cloaca, which is the reproductive opening of the female shark. Once inserted, it opens like an umbrella and anchors the male shark in place for mating. Claspers are also used to determine the sexual maturity of male sharks. The claspers of young male sharks remain soft and flexible, while those of male sharks that have reached sexual maturity have been hardened by calcium deposits, causing them to become rigid and inflexible.