Starfish Skin

Spines, tube-feet and dermis of the Crown of Thorns starfish (Acanthaster planci). It is currently destroying a large portion of the Great Barrier Reef off the coast of northern Queensland, Australia. It has a voracious appetite for coral polyps and virtually no predators.

One of the most bizarre attributes of any life form belongs to the phylum Echinodermata. The name is a combination of Latin and Greek that loosely translates to “having prickly skin”. The more widely known creatures of this phylum include sea stars (starfishes), sea urchins and sea cucumbers. What is so bizarre here, though, is not the prickles and spines that characterize members of the phylum but the processes used to manipulate them.


Here’s The Catch

Echinoderms can use neural signals to manipulate not only muscle tissue but also a connective tissue called "catch collagen". This tissue is a fibrous connective tissue found under the epidermis and is often closely associated with spines other boney plates under the dermis. Unlike muscle tissue it does not contract but changes “state” hence it is also known as a “mutable” collagen. At will, these creatures can move spines or stiffen/loosen their entire outer body without the use of muscles. This is almost certainly beneficial in that they may hold a specific shape or posture without exerting the large amounts of energy required to contract muscle tissue.


"Oh no I'm under attack!"

On a bizarre side-note sea cucumbers (Class Holothuroidea), like this cute little sea pig (Scotoplanes globosa), as well as possessing catch collagen to "liquify" or "solidify" their outer body are able to quickly eject part of their viscera and internal organs out through their anus as a defensive mechanism . Once the predator has taken the bait, as it were, the sea cucumber can hobble off and regrow its insidy-parts.

The sea pig is a sea cucumber that has been secondarily dorso-ventrally evolved so that, while technically it moves around on it's side, tube feet on the "ventral" side have become quite large and concerned with locomotion while tube feet on the "dorsal" side have primarily become sensory in nature.