Scotoplanes, commonly known as the sea pig, is a genus of deep-sea holothurian echinoderm of the family Elpidiidae, order Elasipodida.
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 6 inches/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”. source