Seahorses are unusual because the male carries the eggs until they hatch.

The longer version

Role reversal in seahorses begins with the female transferring her eggs into a sealed brood pouch on the male's abdomen. He fertilises them internally and the tissue lining the pouch swells, supplying oxygen and regulating salinity while the embryos develop.

Parental investment then sits with the male, which frees the female to produce another batch of eggs sooner and raises the total number of offspring a pair can produce. When development finishes, the pouch opens and the male expels dozens to hundreds of fully formed miniature seahorses. Because the young get no further care, size at birth and the quality of the pouch environment largely determine how many survive.

Where this entry sits

This collection gathers small surprises about mammals, reptiles, amphibians, birds, fish, insects, and the pets living alongside people. Expect odd details about senses, anatomy, and everyday behaviour that many people never notice in the animals around them. The full list sits on the Animals page, where every entry is listed in order.