Purple Sea Stars, Part I

Tidepools are their own ecosystem, complete with producers, consumers, and predators. This may leave one wondering, who’s the predator? Clearly there are no fangs or talons among the tidepools’ inhabitants. In tidepools of the Pacific Northwest, it is the purple sea star. Don’t be fooled by their appearance – they are ruthless, carnivorous predators.

Photo Credit – Andrew Reding

Purple sea stars (which actually range in color from brown to orange to purple), are 5-armed invertebrates that can grow to 9 or more inches across. They live on rocky coastlines from California to Alaska. And their favorite prey includes snails, barnacles, mussels, limpets, and even crabs!

For me, this raised the question, how do they do this? Starfish do not have teeth or jaws. So to eat, they pry open shells with their arms. This is where it gets super-weird. Once the prey’s shell is pried open, sea stars stick their stomach out of their mouth. Let me repeat that: starfish push their stomach out of their mouth. Not only that, once they push their stomach out of their own body, they push it into the prey’s shell to digest it before swallowing.

So if the whole eating-stomach thing isn’t weird enough, starfish can regenerate an arm if lost, which is important because they use those arms for eating and for locomotion. Starfish also do not have a brain. Instead they have a simple nervous system that consists of a nerve ring around their mouth. It connects with nerves that extend down each arm and signals them to move. These odd creatures also have neuro-sensory cells over their whole body that relay messages. Odd indeed.