The mouth is at the anterior end of the ventral surface and is surrounded by a ring of twenty tentacles of varying lengths, the tip of each of which has eight projections round the margin.

A further row of peg-like tube feet run along each side and the dorsal surface is dotted with papillae (conical fleshy projections of the body wall with sensory tube feet at their apices) that vary from 2 to 50 mm (0.1 to 2.0 in) in length, the longer ones resembling tentacles.

[3] In the nearly level Porcupine Abyssal Plain in the Atlantic Ocean there is a bed of sediment that has been gradually accumulating for millennia and Oneirophanta mutabilis is one of a number of sea cucumbers that make up about 90% of the megafauna here.

As it progresses it ingests the sediment, processes it through its gut, removes the nutritive organic content and voids the indigestible remains.

The eggs are smaller than 400 μm in diameter with little nutritive tissue present which suggests some form of abbreviated development.