A tube sponge, commonly mauve or purple, sometimes blue, sometimes translucent.

It usually has a very ’serrated’ lip, with a membrane-like structure surrounding the aperture. The lip is thin.

Very often it has a covering of zooanthids or brittle-stars. When it does not, its surface is seen to have a covering of small conical projections.

Gammill (1997) notes three other species: N. erecta which is described as more rope-like, N. amorpha which is encrusting with conical pores, and N. ramosa which is tall and thin, or rope-like.