Hermit crabs that live on land have remnants from when they were in the water, and breathe through their gills and abdominal skin. They can only breathe in moist places.

The orca is said to be the fastest of all cetaceans at 55 km/h.

Penguins are flightless birds, or avifauna. They used to fly in the past, but it is thought that they evolved and stopped flying. Instead, they became good at swimming & diving.

Black teeth may remind you of cavities, but in the case of fur seals, it is a sign of good health.
Black teeth are caused by the presence of good bacteria that produce black pigment in the mouth.
When they are born, their teeth are white, but as they age, they turn black.

Because they have a lot of fat, they are able to maintain their body temperature.