How do starfish just show up in your saltwater fish tank?

Starfish cannot just show up in a saltwater fish tank. They must have been introduced, intentionally or unintentionally. Starfish can be introduced through live rock, which is often collected from the ocean and used in aquariums. They can also be introduced through saltwater that is used to top off the tank or mixed for water changes. In some cases, starfish may be introduced by other aquarium inhabitants, such as hermit crabs or snails.