Although asteroids (starfish) have proliferated in all the world’s oceans for over 500 million years, their evolution remains an enigma. Their characteristic five-rayed shape is familiar in rocky or sandy coasts, in icy seas or in the islands of the Caribbean. Their size can range from one millimeter to one meter. They usually have five arms, but some species can have more than ten, and there are even species with 50 arms. When they have multiple arms, they are often called “sunstars”.
Starfish are solitary animals that move slowly along the seafloor by the action of their ambulacral feet, which are numerous and tiny tentacles located on the underside of the animal. Each foot has a suction cup with an adhesive force of 29 grams. These feet allow them to glide or crawl slowly, turn over when necessary, or bury themselves in sediment. Each ambulacral foot feeds independently from the others through a vesicle. If a starfish is attacked by a predator and loses one of its arms, it will regenerate it, although the arm will be shorter. If the arm is not consumed, it remains alive but will die in approximately one month as it cannot move or catch prey. However, species of the genus Linckia, when they lose an arm, regenerate it by forming four new, shorter arms. These special individuals are known as “comets”.
When a starfish manages to position itself on top of its favorite prey, a bivalve, it wraps its body around it, and the suction cups of its ambulacral feet attach to the valves and start applying pressure to open it. In the past century, it was believed that the starfish hypnotized the mollusk or that it dissolved the shell with acid. However, the reality is even more spectacular. The exhausted mussel loosens its grip and opens the shell slightly. Without wasting time, the starfish extends its own stomach out of its body, applies it to the mussel’s flesh, and begins to absorb and digest it. The complete digestion process takes approximately 10 hours, during which time the stomach remains outside the starfish’s body. Then it will begin its slow journey along the seafloor in search of a new victim.
“You cannot defend what you do not love, and you cannot love what you do not know.”