How do animals without bones move

Question

I cant really visualize how something like a spider or worm or ancient animal like pikaia moved without muscles connected to a ridgid structure like bones, what do the muscles connect to so they work properly?

In: Biology

Answer 1

They are like a water balloon. They have a skeleton only it’s invisible it’s called a hydrostatic skeleton which is a fancy word for meaning that they push off of the bag that holds their guts in.