Ovoviviparity

Ovoviviparity is a reproductive strategy in which embryos develop inside eggs that remain within the mother's body until they are ready to hatch. In this mode, the embryos typically receive nourishment from yolk rather than from a placental connection, and there is little to no direct maternal nourishment during development. The eggs may hatch inside the mother and the young are born alive, or the young may hatch just before or after being released.

This reproductive scheme is distinct from oviparity, in which eggs are laid and hatch outside the body, and from viviparity, in which embryos develop inside the mother with direct maternal nourishment, often via a placenta. Ovoviviparity thus occupies an intermediate position in the spectrum of reproductive strategies, combining internal development with yolk-based nutrition and the absence of prolonged placental support.

Ovoviviparity occurs in several animal groups, most notably among certain reptiles and some cartilaginous fishes, and is observed in a variety of species with different ecological niches. Common examples include boas and many vipers, which retain eggs within the oviducts until near hatching, and the sand tiger shark, where embryos develop internally with yolk as their primary nutrient source.

The strategy can offer advantages such as protection from environmental hazards and predation during development, enabling survival in habitats where external egg-laying would be riskier. It also imposes constraints, such as reliance on yolk reserves and typically smaller litter sizes compared with some oviparous species.