Rays have gill slits on the ventral side of their bodies, while sharks have gill slits on the side of their bodies.

There are five species of wild seals that can be seen in Japan: bearded seal (Erignathus barbatus), ringed seal (Pusa hispida), spotted seal (Phoca largha), Harbor seal (Phoca vitulina), and ribbon seal (Histriophoca fasciata).
In Japan, these seals can basically only be seen in Hokkaido.

The dolphin has a smooth eggplant-like skin to reduce water resistance so that it can swim faster. Incidentally, dolphins renew their skin every two hours.

They have sensory organs called "taste buds" that allow them to search for food. When they spread their whiskers wide, they are looking for food.

It is said that they cannot distinguish colors.