|Scotoplanes globosa and symbiotic lithodid crab|
Elpidia globosa Théel, 1879
Scotoplanes globosa, commonly known as the sea pig, is a species of sea cucumber in the genus Scotoplanes. It has been classified in three different ways. S. globosa are marine animals that belong to the class Holothuroidea, belonging to the higher classification of Echinozoa, which contains both sea urchins and sea cucumbers. Scotoplanes globosa was first described by Hjalmar Théel, a Swedish scientist. Scotoplanes globosa, along with numerous other Holothuroidea were discovered by Théel during an expedition on HMS Challenger between the years of 1873-1876. Scotoplanes globosa was officially described in 1882, 6 to 9 years after its first sighting.
Scotoplanes globosa is most closely related to Peniagone sp. and is also closely related to Cucumaria miniata, commonly known as the red sea cucumber. Scotoplanes globosa descends from Strongylocentrotus droebachiensis, commonly known as the green sea urchin.
Congregations of smaller Scotoplanes globosa are often observed on the ocean floor in groups of 10 to 30. However, groups of Scotoplanes globosa have been observed to be as many as 600 individuals in one congregation. A congregation of Scotoplanes globosa is called a “trawl”. These groups of Scotoplanes globosa often appear to all be facing in one direction, into the ocean current. It is believed that this behavior aids the S. globosa in being able to detect the richest deep-sea feeding sites. S. globosa has also been observed to be the host of multiple deep-sea parasites, such as the small gastropods Stilapex and Crinolamia, and various parasitic crustaceans. These parasites typically bore small holes into the body wall of S. globosa. Scotoplanes globosa are also often accompanied by a symbiotic lithodid crab, the Neolithodes diomedea. It is believed that approximately 22% of Scotoplanes globosa are attended by at least one of these crabs. At this time, scientists are unsure whether the relationship between S. globosa and N. diomedea is mutualistic or commensal.
Scotoplanes globosa is typically 2 to 15 cm in length and appear to be a translucent white color. S. globosa is covered in tube-like feet which are used in locomotion. The tube-like structures found on top of the Scotoplanes globosa are also feet, as opposed to antennae. Scientists are still unsure whether these upper-tube-feet are used in locomotion or used as sensory accessories. They are quite buoyant and are easily displaced by strong currents.
Scotoplanes globosa has a soft, round body with five-to-seven pairs of long, tube-like limbs extending from its body. S. globosa uses these limbs for locomotion. They “walk” along the ocean floor using muscle constrictions to push fluid in and out the tube feet cavities. Scotoplanes is the only genus of holothurians that have been observed to "walk" in this manner.
Distribution and habitat
Scotoplanes globosa are found in almost all deep-sea regions in the world. Specifically, S. globosa live on the abyssal plain. They are commonly found off the coast of San Diego, as well as in the Arctic, Atlantic, Pacific, and Indian Oceans. Scotoplanes globosa typically live at depths of over 1000 meters, and have been found in the deepest locations in the ocean.
Scotoplanes globosa is a deposit feeder, eating detritus which has sunk to the ocean floor. Scotoplanes globosa has been observed to strongly prefer consuming fresh, recently fallen (approximately within the last 100 days) sediments on the surface of the ocean floor as opposed to older sediments. These freshly-fallen sediments are more nutrient-rich. Scotoplanes globosa captures food through its mucous-covered tentacles which surround their mouth. Scotoplanes globosa is also known to congregate around the carcasses of whales which have fallen to the seafloor. It has been discovered that S. globosa utilizes olfaction to locate deep-sea whale carcasses as well as nutrient-rich food sources. These whale carcasses are extremely nutrient-rich and attract many deep-sea creatures, including Scotoplanes globosa.
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