A Gelatinous Deep Sea Swimmer
The Pink See-Through Fantasia is a species of deep-sea swimming sea cucumber with the scientific name Enypniastes eximia. It belongs to the class Holothuroidea, a group that includes all sea cucumbers. Unlike the more familiar, bottom-dwelling varieties, this organism is benthopelagic, meaning it spends time both on the seafloor and swimming in the water column just above it. It has been observed at depths ranging from 500 to over 6,000 meters. First described in 1882 from specimens collected during the H.M.S. Challenger expedition, its full appearance and behavior were not well understood until the advent of deep-diving remotely operated vehicles (ROVs).
The creature's body is gelatinous and composed mostly of water, making it neutrally buoyant. This allows it to float and swim with minimal energy expenditure. Its size ranges from 11 to 25 centimeters (about 4 to 10 inches). The color varies with size; smaller individuals are a distinct bright pink, while larger ones become a darker reddish-brown. Its most notable feature is its translucency, which makes the coiled digestive tract clearly visible through its skin, especially after it has fed.
A Life of Flight and Light
Enypniastes eximia is an active swimmer, a rare trait among sea cucumbers. It uses specialized webbed structures, formed from fused podia (tube feet), to propel itself through the water. A large anterior web acts like a sail or a rowing implement, while smaller posterior veils provide stability. This mobility allows it to travel up to 1,000 meters (3,300 feet) up into the water column to find new feeding grounds or escape threats.
Its diet consists of "marine snow"—organic detritus that sinks from the upper ocean to the seafloor. It lands on the sediment and uses about 20 leaf-like tentacles surrounding its mouth to scoop the material into its gut. The feeding process is remarkably fast; it often spends no more than a minute on the bottom before taking off again. Observers have noted that it sometimes expels the contents of its gut before swimming upwards, a behavior that may reduce its weight like a hot air balloon dropping ballast.
This sea cucumber also possesses a remarkable defense mechanism: bioluminescence. Its skin contains hundreds of granular bodies that produce light when mechanically stimulated. If a predator makes contact, the skin lights up. The fragile skin can also be sloughed off, creating a glowing cloud that distracts the attacker. This has been called a "burglar alarm" strategy, as the light confuses the immediate threat but may also expose that predator to its own hunters in the dark depths. The skin and its luminescent capability can be regenerated.