Sea stars are invertebrate animals and belong to the phylum Echinodermata, from the Greek for “hedgehog skin”, which includes sand dollars, sea urchins and sea cucumbers. Sea stars belong to the family Asteroidea and all have a common characteristic: radial symmetry, i.e. their arms or tentacles radiate from a central point, as in a bicycle wheel. In general, the body is divided into five parts, although there are stars that have more arms.

Sea stars are marine animals with many peculiarities, which could be considered as superpowers!  

They have super powerful feet and can climb walls like Spider-Man!

They move and walk on the seabed, thanks to their ambulacral apparatus, a water vascular system of canals and appendages that runs all over the animal’s body. This apparatus is filled with a liquid very similar in composition to seawater that hydraulically drives fleshy protrusions called ambulacral feet or “tube feet”. The inflow and outflow of water from this water vascular system is regulated by the madreporite, a plate that is placed on one side between two arms and functions as a trap door or sieve through which the water is filtered. The feet not only have a locomotor function, but also a feeding and sensorial function, and they help the animal to firmly attach to the substrate thanks to their suction cups. These secrete an adhesive substance that allows them to move along rocky walls and even the glass walls of an aquarium.  

They can regenerate their body like Deadpool! 

One peculiarity you may not know about sea star is that most of them can regenerate themselves. Yes, you got it right: they can rebuild their lost or injured arms! After the loss of the arm, the missing part regenerates, and it is quite common to find evidence of one, two or more arm regeneration events in almost all individuals in natural populations. 

Basically, regeneration is the ability of an animal’s cells to make new body parts during adulthood, just as they did during embryonic development. Although the process is very complex and not yet 100% understood, it is certain that sea stars use their stem cells to regenerate. Generally, stem cells can differentiate into any type of cell important for the organism, such as blood cells, muscle cells, skin cells, etc. But when stem cells finally differentiate into other cells, they cannot de-differentiate and go back to their initial undifferentiated status. But it seems that sea star cells have this superpower! After receiving a signal, these cells can re-differentiate into all the parts needed to build a completely new limb. And more: one of the best-known examples of regeneration in star seas is the formation of a whole animal from a single arm, termed “comet”.

Because of their fascinating regenerative capabilities, it is not surprising that sea stars have been used as inspirational biological models for innovative regenerative medicine applications.

They can expel their stomach!

Another peculiarity of some sea stars is the ability to pull their stomach out of their body to catch, wrap and digest preys and once finished, finally pull it back inside. This is very useful when eating mussels or other mollusks: thanks to its suction cups, the sea star manages to separate the two parts of the mussel shell. Once it has succeeded in slightly opening the shell, it pushes the stomach out of its body and into the mussel, secreting enzymes that will quickly destroy the prey’s organs, so that…the feast is ready!

Watch this video if you do not believe it:

What about you – what is your superpower?