Starfish do not have bones, but instead have a series of hard plates that provide structure and support to their bodies. Starfish and other critters like them are called echinoderms, or marine invertebrates, which are tailed, finned animals that have backbones — they are not actually fish at all.
Starfish are sometimes referred to by scientists as sea stars. There are around 1,800 different species of star-shaped aquatic creatures. Starfish have a vascular system that runs on water, not blood. It draws sea water into its body and then moves it around through various canals. It is this water that provides the creature's body structure. Starfish can reproduce in two ways: sexually with eggs and sperm being released into the water, or asexually by regenerating.