If you have ever seen a starfish lying on the rocky surfaces of a beach during low tide, these creatures probably seem pretty sedentary. While this may seem true from afar, there is plenty of activity occurring if you get in up close and personal!
On the aboral side of the sea star opposite of the mouth, some sea stars have these amazing tiny claws called pedicellariae that are busy snipping away. These lobster-like pincers act like the cleaners and protectors of sea stars such as the mottled sea star (Evasterias troschelli) and the purple sea star (Pisaster ochraeus). When unwanted debris such as algae settle on these sea stars, their many pincers can clamp onto the algae for removal. Most interestingly, pedicellariae can act as weaponry against unwanted visitors such as the morning star (Solaster dawsoni) and can cause some serious damage to these starfish-eating sea stars if sea stars such as the purple sea star latch on with their many pedicellariae.
Photo of pedicellariae of a sea star. Source: Wikipedia 
Photo of pedicellariae of the purple sea star. Source: Bio 326 team
On the oral side of sea stars where the mouth is located, sea stars have a bunch of tube feet that are full of activity especially since they are used for feeding and moving about. These are essentially tubing that sea stars can fill and empty with water by using the water transport system within their bodies. It creates enough water pressure for these tube feet to extend and help the sea star inch around. With their tube feet, sea stars can even flip their entire bodies around or attach to the shell of a mussel like suction cups to pull them open!
Another highly active part of the sea star are their stomachs! Yes – I say “stomachs” and not “stomach” because sea stars have two! When they pry open the shells of mussels even slightly, they can push out one of their stomachs into a mussel to begin the process of making mussel juice. Since sea stars can’t chew, sipping from mussel shell cups is the perfect solution! In fact, starfish such as the purple sea stars are such voracious eaters of animals such as mussels, barnacles or snails living in the intertidal zone (the area spanning the high and low tide lines) that they are considered a keystone species. This basically means that purple sea stars steal the show in the intertidal zone as their presence or absence can drastically change the players remaining within the community.
Now that you’ve seen some snippets of these amazing creatures in action, are you ready to be part of the action? Be sure to catch these amazing action superstars the next time you pass by the beach!
Check out these cool resources before you meet these action superstars!
Here is an epic video showing how sea stars devour mussels:
Here is a video of the tube feet in action!
Check out this link for more information about pedicellariae: Natural antifouling defences of tropical sea stars – ResearchOnline@JCU
BIOL 326: Experimental biology of invertebrates 