Sea Cucumbers Essay, Research Paper
Sea cucumbers are visual fasinating organisms. To the untrained eye, one may ask wheter the sea cucumber is plant or animal. They are distinguished from the other Echinoderms by the lack of a skeleton that is made up of calcerous plates fixed together. Instead, the soft skin is reinforced with microscopic plates and spicules called ossicles, giving it a leathery texture. All other Echinoderms are radially symetrical, while the sea cucumber posses bilateral symmetry. Characteristics amoung the sea cucumbers tend to be repeated quite frequently, and the different characteristics of species are minimal. The organism can be found in any ocean, shallow or deep, buried in the mud or sand, hidding between rocks, amoungst corals and sometimes even in sponges. They feed on microscopic organisms such as protozoa and phytoplankton. The particles are sensed by the tentacles and then swept into the mouth. Many sea cucumbers injest sand or mud to absorb the organic materials and nutrients. This is the reason why the sea cucumbers are considered to be the earthworms of the sea. Sea cucumbers having tube feet are commonly in the shape of a cylinder. The cylinders posses five bands of radial tube feet running from one end to the other. These are seperated by five interradial bands which tend to have smaller tube feet or are bare. The mouth is surrounded by a tuft of ten to thirty tentacles. The shape and arrangement of these tentacles distinguishes the three orders of tube footed sea cucumbers from one another. The sea cucumbers mouth has a projecting circular lip. It is followed by a large pharynx which is surrounded by a crown of calcareous plates. The plates are made up of five radial parts and five to fifteen interradial parts. The elasticity of the calcerous plates is because the plates are so loosly connected. Connected to the radial plates are five large muscles the may travel the whole length of the organisms body. The pharynx is connected to a small muscular stomach by an esophagus. The stomach is then connected to a long intestine that coils and loops everywhere within the body cavity. The intestine ends at the cloaca and anus, usually opposite the mouth. The intestine is attached to the body cavity wall by mesenteries. The Echinoderms use a water vascular system for respiration, excretion, locomotion, and food capture. The sea cucumbers water vascular system is very different from the rest of the Echinoderms in that it is more developed, uses bodily fluid instead of sea water and is built on a pentaradial plan. In addition, unlike the others, the sea cucumber’s madreporite lies free within the coelom. The madreporite is the structure used for water intake. The water vascular system consists of a ring canal behind the mouth. Five radial canals extend to the tube feet and very small branches connect to the ampullae. The ampullae control movements of the tentacles. One or more small sacs (Polian vesicles)
are attached by slender stalks to the ring canal. The madreporite takes in the water and only exceptionally is it fixed to the wall. The respiratory trees are two tree-like branches that reach far within the body cavity. Sea water is pumped in and out of the trees by subtle muscular actions of the cloaca. The water then is emptied into the body cavity where it mixes with body fluid and supplements the fluid with oxygen. The respritory trees are also needed to remove carbon dioxide as well as other unwanted waste products. In additon, the respiratory trees may also take part of the excretory functions. In sea cucumbers, the sexes are seperate; some are hermaphroditic, having both sexes. They have only one gonad which is considered to be a very primitive characterisitic of the Echinoderms. Fertilization is external and the free swimming larva is called an auricularia. The reproductive organs are microscopic in size. When attacked or threatened, some species will eject certain organs such as the respiratory tree and the alimentary tract, through their anus. This clouds the water with a mucous that predators get caught or lost in. Within six weeks to two months the organs are completely grown back. This mechanism of defense shows the great regeneration powers that the sea cucumbers posses. Other organisms have symbiotic relationships with the sea cucumber. The sea cucumber is sometimes a host to the pearl fish, which slides backwards into the respiratory openings of sea cucumbers. Sometimes a pearl fish will spend it’s entrie life with one individual. Together, they form a commensal relationship, one in which no harm is done to the host. Another commensal relationship is the sea cucumber and a small fish named Carapus. This fish uses the inside of the sea cucumber as shelter. Sea cucumbers are prized in Asian markets as well as worldwide as an ingredient in cuisine. They are usually boiled, dried or made into a gelatinous soup that are gourmet luxuries amoung the Chinese, Japanese, Malayans, and other oriental peoples. It is said that when eaten, the sea cucumber has aphrodisiac qualities and could be a suppresant of musculoskeletal inflammatory diseases. The sea cucumber was once very common thoughtout the worlds oceans, but has greatly decreased due to the demands of the Asian market. While sea cucumbers in the Gal pagos have not aroused much interest in the past, scientists now fear that the rapid decline in populations of these relatively unglamorous animals may have serious affects on other species that are part of the same complex food web. Sea cucumbers are interesting organisms. They can be found in any ocean. They are unique to the Echinoderms because of their bilateral symmetry, the lack of a hard endoskeleton, and they posses a very advance water vascular system. Thyone briareus, a more advanced sea cucumber, is unique to the other sea cucumbers because of its widely distrubute calcareous plates and water vascular system with hemoglobin present. Sea cucumbers have been said to have benefical qualities when eaten and because of this they are in high demand. The demand of this organism has taken an obvious toll on the abundance of sea cucumbers the world’s oceans’ once possessed.