
Today, let us look at some
sea cucumbers at the ocean floor if the Great Barrier Reef in Australia.
Most of us know that Sea cucumbers (海參) are marine animals with a leathery skin and an elongated body containing a single branched gonad. They are found worldwide on the sea floors. There are a number of holothurian species and genera, many of which are targeted for human consumption.
It is interesting indeed that sea cucumbers communicate with each other by sending hormone signals through the water.
A remarkable feature of these animals is the catch collagen that forms their body wall. This can be loosened and tightened at will. If the animal wants to squeeze through a small gap, it simply liquefies its body and pours into the space. To keep itself safe in these crevices and cracks, the sea cucumber hooks up all its collagen fibres to make its body firm again.
Some species of coral-reef sea cucumbers can defend themselves by expelling their sticky cuvierian tubules to entangle potential predators. When startled, these cucumbers may expel some of them through a tear in the wall of the cloaca in an autotomic process known as evisceration. Replacement tubules grow back in one-and-a-half to five weeks, depending on the species. The release of these tubules can also be accompanied by the discharge of a toxic chemical known as holothurin, which has similar properties to soap. This chemical can kill any animal in the vicinity and is one more way in which these sedentary animals can defend themselves.
Like sea urchins, most sea cucumbers have five strip-like ambulacral areas running along the length of the body from the mouth to the anus. The three on the lower surface have numerous tube feet, often with suckers that allow the animal to crawl along. The two on the upper surface have under-developed or vestigial tube feet, and, in some species, lack tube feet altogether.
In those sea cucumbers that lack regular tube feet, those immediately around the mouth are always present. These are highly modified into retractile tentacles, much larger than the regular tube feet. Sea cucumbers have between ten and thirty such tentacles, depending on the species.