Sexual reproduction is most common type of reproduction among the plants and animals. They are of following types;
1) Syngamy: The fusion of gametes takes place completely, if male and female gametes are produced by same cell or organism and both gametes fuse together to form a zygote, this is called as Autogamy, paramecium is its example. Another is Anisogamy in which some organisms produce two types of gametes. Both types of gametes differ from each other in their shape and size and are known as an isogametes or heterogametes. Male gametes are motile and small in size and are known as micro gametes. Female gametes are passive and have large size and are known as macro or mega gametes. The union of micro and mega gametes is known as anisogamy.
2) Conjugation: It is temporary union of two individuals of same species. During the union both individuals known as conjugants exchange certain amount of nuclear (DNA) material and after this conjugants are separated e.g. Paramecium.
The fertilization may be internal or external. It depends on organism and its environment in which that animal live. In external fertilization many invertebrates simply release their gametes into water in which they live and allow them to fertilize (e.g. sponges and corals), while in some other invertebrates utilize internal fertilization to transfer sperm
…show more content…
Internally fertilized eggs are deposited in gelatinous mass. The large, yolky egg of terrestrial snails are deposited in moist environments, such as leaf litter, and a calcareous shell may encapsulate them. In marine gastropods, spiral cleavage results in free swimming trochophore larva that develops into another free swimming larva with foot, eyes, tentacles, and shell called a veliger larva. Sometimes, the trocophore is suppressed, and the veliger is primary larva. Torsion occurs during the veliger stage, followed by settling and metamorphosis to the