Ovoviviparity

The characteristic quivering abdomen caused by movement of tadpoles within a pregnant female Limnonectes larvaepartus.

Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos that develop inside eggs remain in the mother's body until they are ready to hatch. Ovoviviparous animals are similar to viviparous species in which there is internal fertilization and the young are born live, but differ in that there is no placental connection and the unborn young are nourished by egg yolk; the mother's body does provide gas exchange (sharks and rays). The terms "ovoviviparity" or "aplacental viviparity" have been deprecated because they encompass several unrelated modes of reproduction. In some species, the internally developing embryos rely solely on yolk. This is known as "yolk-sac viviparity" and is regarded as a type of lecithotrophy (no maternal provisioning).

Other species exhibit matrotrophy, in which the embryo exhausts its yolk supply early in gestation and mother provides additional nutrition. This additional provisioning may be in the form of unfertilized eggs (intrauterine oophagy), uterine secretions (histotrophy), or it may be delivered through a placenta. The first two of these modes were categorized under aplacental viviparity.^[1]

Amphibians

The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother. Five modes of reproduction can be differentiated ^[2] based on relations between zygote and parents:

• Ovuliparity: fecundation (fertilisation) is external (in arthropods and bony fishes, most frogs)
• Oviparity: fecundation is internal, the female lays zygotes as eggs with important vitellus (typically birds)
• Ovo-viviparity: or oviparity with retention of zygotes in the female's body or in the male's body, but there are no trophic interactions between zygote and parents. (Anguis fragilis is an example of ovo-viviparity). In sea horse, zygotes remain in the male's ventral "marsupium". In the frog Rhinoderma darwinii, the zygotes developed in the vocal sac. In the frog Rheobatrachus, zygotes developed in the stomach.^[3]
• Histotrophic viviparity: the zygotes develop in the female's oviducts, but find their nutriments by oophagy or adelphophagy (intrauterine cannibalism in some sharks or in the black salamander Salamandra atra).
• Hemotrophic viviparity: nutriments are provided by the female, often through a placenta. In the frog Gastrotheca ovifera, embryos are fed by the mother through specialized gills. The lizard Pseudomoia pagenstecheri and most mammals exhibit a hemotrophic viviparity.

Ovolarviparity

Some insects, notably tachinid flies are ovolarviparous, which means the embryos develop into the first larval stage (instar) within eggs while still in the female's oviduct. As a result, larvae hatch more rapidly, sometimes immediately after egg deposition, and can begin feeding right away. A similar phenomenon is larviparity, in which larvae hatch before the female delivers them, although this may be mistakenly identified in species with very thin and transparent egg membranes.^[4][5]

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