THE DIFFERENT TYPES OF REPRODUCTION FEATURES IN SHAREK 1711503 安然

Mating methods In these cases the fertilization is internal. At the back of the pelvic fins are the male reproducetive organs called claspers（鳍脚）, which transfer the sperm to the female. The mating usually consists of the insertion（插入） of the clasper within the oviduct （输卵管）. In some species, male sharks hold firmly to the female but in other species both swim together while mating. Courtship（求爱） processes are also varied, but it is common that the male bites the female shark to get its interest or to immobilize（使固定） it.

There are three reproductive methods 1.Oviparity 2.Ovoviviparity 3.Viviparity

Oviparity Compared with the viviparity, Oviparity only takes a small part of the reproduction. These eggs are round to oval and are encased in a hornlike（似角的） egg capsule （胶囊）. The protective egg capsules are composed of two to three cases and often have interesting shapes, e.g. cordlike（带状的） growths which serve to anchor（使 固定） the eggs on water plants or other objects. This prevents the eggs from being swept away. Normally the eggs are quite large, measuring 10 to 25 cm in length. They also have a large yolk which nurtures the embryos（胚胎） sufficiently with nutrients. By laying their young in well protected, stable（稳定的） egg capsules with sufficient nutrients, the female sharks shorten the time needed to care for their young. Example : Atelomycterus marmoratus(斑鲨)，Heterodontus zebra（狭纹虎鲨）

Example:Carcharodon carcharias(大白鲨) Rhincodon typus （鲸鲨） Ovoviviparity Most sharks are ovoviviparous, meaning that the eggs hatch（孵化） in the oviduct within the mother‘s body and that the egg’s yolk and fluids（流体） secreted（分泌） by glands in the walls of the oviduct nourishes（滋养） the embryos. The young continue to be nourished by the remnants（残留物） of the yolk and the oviduct‘s fluids. As in viviparity, the young are born alive and fully functional. Lamniforme sharks（鼠鲨目） practice oophagy（食卵性）, where the first embryos to hatch eat the remaining eggs. Taking this a step further, sand tiger shark （锥齿鲨） pups cannibalistically（同类相食的） consume neighboring embryos. The survival strategy（战略） for ovoviviparous species is to brood the young to a comparatively large size before birth. The whale shark is now classified as ovoviviparous rather than oviparous, because extrauterine（子宫外的） eggs are now thought to have been aborted（流产）. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs（礁石）. They choose such areas for protection from predators（捕食者） (mainly other sharks) and the abundance（充裕的） of food. Dogfish （星鲨）have the longest known gestation period（孕期） of any shark, at 18 to 24 months. Basking sharks （姥鲨） and frilled sharks（皱鳃鲨） appear to have even longer gestation periods, but accurate data are lacking.[66] Example:Carcharodon carcharias(大白鲨) Rhincodon typus （鲸鲨） Cetorhinus maximus（姥鲨）

Viviparity Viviparity is the gestation of young without the use of a traditional egg, and results in live birth. Viviparity is sharks can be placental or aplacental. Young are born fully formed and self-sufficient. Hammerheads, the requiem sharks (such as the bull and blue sharks), and smoothhounds are viviparous. Example:Negaprion queenslandicus(柠檬鲨) sphyrnidae（锤头双髻鲨）