How does a yolk-sac placenta nourish some developing sharks?

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Shortfin mako shark swimming in clear blue water near the surface off the West Coast of New Zealand, mouth slightly open showing teeth. — shark Shortfin mako shark (*Isurus oxyrinchus*), found throughout tropical and temperate seas worldwide.

In viviparous shark species, the yolk-sac placenta serves as a vital structure for nourishing the developing embryo. This process occurs when the yolk sac develops specialized folds and projections that interdigitate—or lock together—with corresponding folds of the mother's uterine wall.12

Through this intimate association between the vascular embryonic yolk sac and the vascular maternal uterine wall, nutrient material is efficiently passed from the mother to the developing shark. This mechanism allows the mother to provide essential nourishment directly to the young during their development within the uterus.12