Stayin' Alive: Adaptations

Water-Vascular System

The water-vascular system is a trait that all echinoderms possess. It is a system which fluid is taken in through a pore and circulated through a system of canals. The fluid is then used to extend out a tube-foot which helps the organism move and feed. The system developed in holothurians is very comparable to the water-vascular system found in other echinoderms such as sea stars, however there is no madreporite (the pore that allows water into the water-vascular system) on the outside of the body wall to allow sea water into the ring canal of the system. Instead of circulating sea water throughout the canals of the system, the water-vascular system of a sea cucumber relies on the coelomic fluid inside of its body. The madreporite which is usually located on the outside of echinoderms lies within the coelom just below the holothurian’s pharynx.  That madreporite takes in coelomic fluid which then travels to the ring canal and then to the radial canals which are ligned with ampullae.  The radial canals direct the fluid into the ampullae which resemble small pipettes.  When the top of the ampullae are constricted they extend the podia, or tube feet, down to the substrate.  This system is not only important for locomotion but also for feeding since the tentacles surrounding the mouth of sea cucumbers (see photos below) are also elongated podia which rely just as much on the water-vascular system as the rest of the podia do.

                                                                 RespiratoryTrees

Unlike other echinoderms, the sea cucumber possesses respiratory trees. These are structures sea cucumbers have developed in order to breathe oxygen. The structures which are simply deep invaginations into the body of the holothurian, are similar to simple lungs; however, rather than taking in air through the mouth, the respiratory trees draw in and expel water from the cloaca or anus. The respiratory trees then absorb oxygen from the water which is then to be distributed throughout the body. In addition to being a beneficial and crucial organ to sea cucumbers, it also provides housing for an organism called Pearlfish. This structure is very well developed in the species Stichopus chloronotus

Catch Connective Tissue

Catch connective tissue is the name given to connective tissue in holothurians and is often times referred to as mutable collagenous tissue. It is believed that this tissue is able to contract and expand under the control of the nervous system and can cause their bodies to become extremely stiff, or in some cases, like in the case of Stichopus chloronotus, it can possibly cause its body to soften to the point where the body will liquify and drip between your fingers. This will more than likely result in the death of the organism. The function of this tissue has been thought to be mainly associated with locomotion; however, Stichopus chloronotus is capable of shedding this same catch connective tissue rather easily when attacked by a predator. For this reason, it has been thought that this tissue could be used as a defense mechanism. See the page on interactions to learn more about this.  Along with this, Stichopus chloronotus is able to divide itself much more easily than other holothurians capable of asexual reproduction.  This tissue could help play a role in the ease at which Stichopus chloronotus is able to perform transverse fission. Click here to learn more about this interesting method of reproduction.    

 

Keep going to find out how Stichopus chloronotus provides itself with nutrients!

Or, check out some other great organisms at Multiple Organsims!