The class Holothurioidea comprises about 1100 species, 380 of which are from the deep sea, i.e. from depths exceeding 200-400 m. Among the five orders, the Elasipoda are unique in being confined to the deep sea.
The knowledge of the Elasipoda was founded by the Challenger Expedition 1872-1876. Also the subsequent exploration of the group was based on the collections from the great deep-sea expeditions.
The material collected by the Galathea Expedition 1950-52 is larger than that of any previous expedition. This is due to the use of large collecting gear, SUCH as Herring Otter Trawl, and Sledge Trawls with 3 and 6 m wide openings. Large gear is especially suited for the catch of holothurians, which, owing to their high buoyancy, often escape the openings of smaller nets. Its effectiveness is shown by the fact that only one out of a total of 80 soft-bottom stations at depths greater than 1000 m failed to bring up holothurians.
The present work describes the Elasipoda collected by the Galathea, as well as a small number of Elasipoda collected by the late Dr. Th. Mortensen. In addition, the work is based on a re-examination of the material from most of the previous deep-sea expeditions.
The Systematic Part includes all the known species of the four benthic families of Elasipoda (the pelagic family, Pelagothuriidae, is omitted). The number of recognized species is reduced from 165 to 106, despite the erection of 11 new species. The order is being divided into two suborders, Deimatina and Psychropotina, the foundations of which are presented in the General Part.
The General Part deals with the morphology. biology, and distribution of the Elasipoda. Special chapters are devoted to the problems of the hadal fauna and to the evolutionary processes in the deep sea, as viewed from our present knowledge of the Elasipoda.