This week in Lembongan… An often over looked sea creature by experienced divers and a creature that our guides rarely point out. But very often while teaching PADI Open Water courses or diving with first time divers we get the full finger point and a shrug of the shoulders when passing by these strange sea cucumbers. Sea cucumbers come in many different colors, shapes and sizes, some very plain and others that look like something out of an alien movie.
Sea cucumbers are found on the sea floor worldwide with the greatest number being in the Asia Pacific region. Many of these are gathered for human consumption and some species are cultivated in aquaculture systems. The harvested product is variously referred to as trepang. Sea cucumbers serve a useful role in the marine ecosystem as they help recycle nutrients, breaking down detritus and other organic matter after which bacteria can continue the degradation process.
Most sea cucumbers, as their name suggests, have a soft and cylindrical body, more or less lengthened, rounded off and occasionally fat in the extremities, and generally without solid appendages. Their shape ranges from almost spherical for “sea apples” to serpent-like for Apodida or the classic sausage-shape, while others resemble caterpillars.
Sea cucumbers have no true brain. A ring of neural tissue surrounds the oral cavity, and sends nerves to the tentacles and the pharynx.The animal is, however, quite capable of functioning and moving about if the nerve ring is surgically removed, demonstrating that it does not have a central role in nervous coordination. In addition, five major nerves run from the nerve ring down the length of the body beneath each of the ambulacral areas.
Most sea cucumbers have no distinct sensory organs, although there are various nerve endings scattered through the skin giving the animal a sense of touch and a sensitivity to the presence of light. There are, however, a few exceptions; members of the Apodida order are known to possess statocysts, while some species possess small eye-spots near the bases of their tentacles.