This is a juvenile starfish, but don't let its adorable, diminutive size mislead you.
Some starfish, like the morning sun star, grow up to be voracious predators, feasting on other sea star species. As an adult, the morning sun star can reach a diameter of 15 inches and have anywhere from 8 to 16 arms, or rays. Many other sea star species will try to "run" out of the way when it approaches, or even have developed strategies for fighting back, including using small pincers to ward off the attacking morning sun star or inflating so that it can't get a grip. But though it sounds like a rather vicious sea star, the morning sun star has an important role to play in controlling the populations of other sea stars and balancing out the ecosystems in which it lives.