Sylvain Cordier / Emperor penguin (Aptenodytes forsteri), chick in brood pouch of parent, Snow Hill Island, Antarctic Peninsula

Doug Allan / Two-week-old Emperor penguin chick sits on parent's feet under brood pouch for warmth {Aptenodytes forsteri} Antarctica

Alex Mustard / Common seahorse (Hippocampus kuda). The dark patch beneath his snout is his brood pouch. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Stefan Christmann / Emperor penguin (Aptenodytes forsteri) feet, adult brooding unseen recently hatched chick in brood pouch. Atka Bay, Antarctica. August.

Stefan Christmann / Emperor penguin (Aptenodytes forsteri) brooding chick aged six to eight weeks. Atka Bay, Antarctica. September.

Constantinos Petrinos / Estuary seahorse (Hippocampus kuda) adult male, with brood pouch. Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Estuary seahorse (Hippocampus kuda) adult male with brood pouch. Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Harlequin ghost pipefish (Solenostomus paradoxus) female with eggs in the brood pouch. Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Harlequin ghost pipefish (Solenostomus paradoxus) female with eggs in the brood pouch. Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Harlequin ghost pipefish (Solenostomus paradoxus) female with eggs in the brood pouch. Lembeh Strait, North Sulawesi, Indonesia.

Ingo Arndt / Christmas Island Red Crab (Gecarcoidea natalis) eggs in females opened brood pouch shortly before spawning / Christmas Island, Indian Ocean, Australian Territory

Sylvain Cordier / Emperor penguin (Aptenodytes forsteri), chick protected by adult in brood pouch, Snow Hill Island, Antarctic Peninsula