Friction.
Animals like sea urchins, some species of pufferfish, and certain types of crabs are not streamlined. Their body shapes are more round or bulky, which can make them slower swimmers compared to streamlined animals like dolphins or sharks.
It's shape.
an animal, car or boat are streamlined because most animals, cars or boats have round corners and they are low to the groung this means that they go faster because streamlining helps us go faster and the rounder a shape is the faster it will go
octopus and star fish
sea urchin
Yes, if you're comparing it to a buffalo.
Whale
the catfish
killer whale
...
The cheetah is the most streamlined big cat.