1. Sea stars use hydraulics to get around. The tube feet lining the arms of sea stars help the animal move along through a “water-vascular system” in which seawater is circulated through the body and into the tube feet to extend them.
Some species use this system for some seriously speedy movement. According to NOAA, "Adult sunflower sea stars can move at the astonishing speed of one meter per minute using 15,000 tube feet."
2. Sea stars can produce glue with their tube feet. Not only do they have suction power, but they have glue power too. A tube foot can release a glue to have extra solid grip on rocks or prey, and then release a solvent for when the sea star wants to let go.
The Echinoblog has a great visual explanation of how this whole process works, and notes: "It turns out that the whole chemistry and physical processes of tube foot adhesion is actually quite complex and has very useful applications in adhesives, glues and so forth."
3. Sea stars can eat oysters and clams by putting their own stomach inside the barely opened shells of the living prey. Using those tough tube feet, sea stars can pry open the shells of oysters and clams, which alone takes an impressive amount of suction power. When the sea star opens the shell even only just 0.25 millimeters, it extrudes its stomach through its mouth and inserts it inside the shell of the prey. It starts the digestion process there, liquifying the prey before it consumes it through its small mouth. Gross, and also completely amazing.
4. Sea stars have eyes on the end of each arm. Rather than placing eyes in a central location, sea stars make the most of their arms for taking in the ocean around them. At the tip of each arm is one teensy eye, which can be used to sense light or dark. The eyes aren’t exactly well developed, but they are used for navigation.
“An investigation by Anders Garm from the University of Copenhagen and Dan-Eric Nilsson of Lund University showed how blue starfish would move around in an undirected manner until coming within 2 meters (6.5 ft) of a reef,” writes Christopher Stevens. “Visually sensing the reef, the sea stars would make a beeline for their desired environment. The light-detecting cells work slowly, and sea stars are color-blind, but it appears that steady images such as reefs stand out as dim splotches to guide the animal.”
5. Sea stars can change sex back and forth from male to female as needed. There are several species of animal that can change sex if needed, such as when there is an abundance of females but no males during breeding season. Sea stars are one such creature, but what makes them even more amazing is they can switch sex back and forth if necessary. If a sea star starts life as a female but needs to switch to being male, it can still switch back to female again if the need arises.