There are 28 main types of animals, or phylla. Only one type of animal, the sub-phyllum "Vertebrates", has a spine like ours. In other words, we are more closely related to an ordinary fish than that fish is to a starfish or jellyfish.
All vertebrates have a spine down the middle, and the left side looks like the right side. This is called "mirror symmetry" or "bilateral symmetry". So you'll never see a vertebrate with 5 arms (like a starfish), or 8 arms (like an octopus), or a lot of tentacles (like a jellyfish). Vertebrates don't move like those animals either.
Sharks are fish. Like all fish, they wag their tails side-to-side to swim.
Dolphins and whales are mammals. They swim by waving their tails up and down
These furry mammals have big hind feet for swimming and steering