Diagnosis : Tentacles shield-shaped, retractor muscles and respiratory trees absent. Tubefeet usually present. Body bilaterally symmetrical. Calcareous deposits include pointed rods or their derivatives, wheels, cruciform bodies, or are lacking altogether.

Remarks: Most elasipods are exclusively deep-sea forms, living on a soft bottom, although some species are bathypelagic in habit. As a result of several deep-sea expeditions the elasipods have been well described by many workers (Theel, 1882; Ludwig, 1894; Sluiter, 1901b; Koehler and Vaney, 1905; Ohshima, 1915; Herouard, 1923; Heding, 1940; Madsen, 1953; Hansen, 1956, and others), and the group at present contains over 100 species. It is likely that many more species are yet to be discovered.

Currently, five families are recognised. These may be distinguished as follows:

1 (2)	Body ovoid, gelatinous, lacking calcareous deposits. Usually a large brim developed anteriorly	Pelagothuriidae (p. 27)
2 (1)	Body bilaterally symmetrical. No conspicuous anterior brim. Calcareous deposits present.
3 (4)	Elongate nonretractile lateral processes present. Skin usually thin, parchment-like or brittle	[Deimatidae]
4 (3)	Lateral processes lacking; skin usually thick, gelatinous.
5 (6)	Calcareous deposits include wheels	Laetmogonidae (p. 19)
6 (5)	Wheels lacking.
7 (8)	Calcareous deposits most commonly include straight or curved rods, three-armed spicules, rarely minute netlike plates, rosette-shaped or elliptical bodies	Elpidiidae (p. 30)
8 (7)	Deposits simple rods or four-armed bodies, with inwardly curved arms and often an outer central projection	Psychropotidae (p. 27)

Of these five families, all but the Deimatidae are so far known from the New Zealand region. It is expected that the Deimatidae will eventually be discovered here, as the family has a cosmopolitan distribution.