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Enypniastes eximia (Echinodermata | Holothuroidea) is an important member of the benthic boundary layer community in deep waters. Like most holothurians [sea cucumbers] it feeds on sediments at the bottom of the ocean. Unlike most sea cucumbers, it isn’t sessile: it swims.
Holothurians⇔ sea cucumbers
Benthic boundary layer ⇔ the sediment at the bottom of a river | lake | ocean and the layer of water directly above it.
Benthic ⇔ the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Benthic organisms generally live in close relationship with the substrate bottom and many are permanently attached to the bottom.
It can be found in every ocean, 500 - 5,000 meters deep and is able to swim up 1,000 meters using front and back swimming structures.
E. eximia finds food by using the tentacles surrounding its mouth to pick up sediments from the sea floor, from which it extracts the attached edible organic material.
When threatened, the swimming sea cucumber can cover its entire body in a bioluminescent glow. Direct observations have shown how this bioluminescence is produced. It is triggered mechanically - when the animal is physically contacted or impacted by something.
Light emission in this species appears to serve as ananti-predatory strategy, in the sense of being a ‘burglar alarm’. In its dark, near-bottom habitat, physical contact by a predator elicits light production which reveals the presence of the attacker to [the predator’s] own visually-cued predators. The luminescent surface tissue then easily sloughs off, which may also serve to confuse the predator.
Sea cucumbers serve a useful purpose in the marine ecosystem as they help recycle nutrients, breaking down detritus and other organic matter after which bacteria can continue the degradation process.
Some information from Bruce H. Robison, ”Bioluminescence in the benthopelagic holothurian Enypniastes eximia" in Journal of the Marine Biological Association of the United Kingdom, May 1992. [ abstract ]