The Bathyal Holothurians of the New Zealand Region
[Introduction]
Diagnosis: Tentacles 8–30 in number, not branched but digitiform or digitate, the digits sometimes bifurcate. Retractor muscles, tubefeet and respiratory trees present. Calcareous ring simple, lacking complex posterior processes. Body U-shaped, enclosed in a test comprising imbricate plates.
Remarks: Of the three families (Ypsilothuriidae, Rhopalodinidae and Vaneyellidae) included in this order (Pawson and Fell, 1965, p. 2) only the Ypsilothuriidae is well represented in bathyal depths.