A new class of Echinodermata from New Zealand

Abstract

During examination of echinoderms from sunken wood collected from depths between 1,057 and 1,208 m off the New Zealand coast, we discovered nine specimens of a small flattened discoidal invertebrate. These animals, briefly described here, superficially resemble a cnidarian medusa, but their pentamerous morphology is distinctly echinoderm-like. We consider that the features of these newly discovered echinoderms warrant the recognition of a new class. Xyloplax medmiformis n.gen. and n.sp. represents a radical departure in morphology from any other known extant echinoderm. Its obvious tube feet, clearly pentamerous body pattern, and calcite skeleton leave no doubt that the animal is an echinoderm. However, its concentrically arranged skeletal structures and single series of tube feet arranged in a ring are novel. The water vascular system of Xyloplax consists of a double ring of canals which service the tube feet in inter-radial positions; in all other living echinoderms the vascular ring (circum-oral) is single, and the tube feet are serviced from it in radial positions. These specimens represent the first new class of living echinoderms to be described since 1821. A full description of the new taxon is in preparation.