Seahorse
Seahorses are unique because the male hatches the eggs in a pouch on his belly. The female inserts her ovipositor into the male’s brood pouch. She places dozens to thousands of eggs in the pouch. As the female releases her eggs, her body slims while his swells. The male releases his sperm directly into the water. The sperm then fertilize the eggs in the pouch. The fertilised eggs are then embedded in the pouch wall. They get nutrition and oxygen from the fluid in the pouch. In the pouch, the salinity of the water is controlled. This prepares the newborns for life in the sea.