The Elpidia glacialis (1876)

Phylum : Echinodermata Subphylum : Echinozoa Class : Holothuroidea Order : Elasipodida Family : Elpidiidae Genus : Elpidia Species : E. glacialis

Members of the Elpidiidae have particularly enlarged tube feet that have taken on a leg-like appearance, and are the only instance of legged locomotion amongst the holothurians, using water cavities within the skin (rather than within the leg itself) to inflate and deflate the appendages. These legs, in conjunction with their large, plump appearance (about 15 cm long) have suggested the common name "sea pig". There are other genera of Elpidiidae with a similar appearance that have also been referred to as "sea pigs".

Elpidia live on deep ocean bottoms, specifically on the abyssal plain in the Atlantic, Pacific and Indian Ocean, typically at depths of over 1000 meters. Some related species can be found in the Antarctic. Elpidia (and all deep-sea holothurians) are deposit feeders, and obtain food by extracting organic particles from deep-sea mud. Elpidia has been observed to demonstrate strong preferences for rich, organic food that has freshly fallen from the ocean's surface, and uses olfaction to locate preferred food sources such as whale corpses.

Scotoplanes, like many sea cucumbers, often occur in huge densities, sometimes numbering in the hundreds when observed. Early collections have recorded 300 to 600 individual specimens per trawl. Sea pigs are also known to host different parasitic invertebrates, including gastropods (snails) and small tanaid crustaceans.