Hydrostatic skeleton

Okay kiddo, have you ever played with a water balloon? Remember how it felt kind of soft and squishy, but it would always stay in the same shape no matter how you moved it around? Well, that's kind of what a hydrostatic skeleton is like!

In some animals, like worms and jellyfish, they don't have any bones or hard parts to hold them up. Instead, they have something called a hydrostatic skeleton. Which means that their body is basically filled with water or another kind of fluid and it helps hold them up and move them around.

Think of it like a water balloon again, but instead of just being a round shape, the animal can change its shape by contracting its muscles and squeezing the fluid inside to make different parts of its body move. So if it wants to stretch out and move along the ground like a worm, it can squeeze the fluid in its body to help it reach forward.

Overall, a hydrostatic skeleton isn't something you can see on the outside of an animal, but it's really important for helping them move and stay upright without any bones.