Accounting for as much as 90 percent of the biomass in marine environments at depths of 5.5 miles and deeper, sea cucumbers are one of the ocean’s most prolific species. Named for their tuberous and bumpy resemblance to cucumbers, these extraordinary creatures are part of the recycling process that occurs in the ocean, processing detritus and decaying organic matter into smaller particles that will continue down the line to be further degraded by bacteria. Sea cucumbers share the same lineage with other Echinoderms, which includes sand dollars, sea urchins, and starfish.
Although most sea cucumber locomotion is facilitated by tube feet or contracting muscles on the seafloor, the bodies of some species are made of a tougher gelatinous tissue that allows buoyancy control, and therefore, propulsion through the water column. At the anterior end of every sea cucumber is a mouth, surrounded by a ring of tentacles that can be retracted into the mouth. These tentacles consist of a single branch or many, which sift through the substrate and bring food into the mouth, or are thrust out into the water column to catch drifting plankton. A colony of 33 specimens per square yard, a quantity often found in the South Pacific, can process 34 pounds of sediment annually. If that doesn’t seem like much, consider the vastness of the ocean and the microscopic nature of their primary food source!
One of the most astounding features of the sea cucumber is its “catch” collagen. The rigidity of this catch collagen is controlled neurologically, which means these animals can soften and harden it at will, which comes in very handy for escaping predators in small crevices. The sea cucumber will loosen up all this collagen until it can easily move into the desired space. When it feels it is safe, it simply re-hardens the collagen and bides its time until it goes on the move again. Although all Echinoderms have catch collagen, it is not as unusual to observe in other species.
Top image via stefanie says