Ovoviviparity

Ovoviviparous animals are those animals that are similar to viviparous species in which there is internal fertilization and the young are born alive, but differ in that there is no placental connection and the unborn young are nourished by egg; the mother's body does provide gas exchange. 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 the 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 histotroph viviparity, or aplacental viviparity. ==Examples==

Fish In seahorses, zygotes remain in the male's ventral "marsupium". Amphibians The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother. Modes of reproduction include based on relations between zygote and parents: • Ovuliparity: external fertilisation, as in arthropods, many bony fishes, and most amphibians • Oviparity: internal fertilisation, where the female lays zygotes as eggs with important vitellus (typically birds) • Ovoviviparity can be thought of as a form of oviparity where the zygotes are retained in the female's body or in the male's body, but there are no trophic interactions between zygote and parents. This is found in Anguis fragilis. In the frog Rhinoderma darwinii, the zygotes develop in the vocal sac. In the frog Rheobatrachus, zygotes developed in the stomach. ==Ovolarviparity==

Some insects, notably tachinid flies, are ovolarviparous, which means that the embryos develop into the first larval stage (instar) within the eggs while still in the female's oviduct. As a result, the 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. ==Criticisms and disuse==

A lack of a rigidly defined term resulted in widespread misuse of the term ovoviviparity in the biological literature. Ovoviviparity has been used to describe delayed forms of egg-laying reproduction as well as live-bearing species that provide maternal nutrients but do not use a placenta. ==References==