Identified and confirmed by Richard Willan

Identity suggested by Richard Willan who also commented that the common rhinophore pocket is an aberration.
"It's mightily interesting because of the presence, on the mantle, of two types of pustules – taller unpigmented ones (that don't
seem to have any emergent spicules, so they can't be true caryophyllidia), and lower and smaller opaque white ones.
Now that is very unusual. Externally to me it's a Cadlina sp. (Cadlinidae), but it doesn't match any of the
Cadlina spp. previously named/known from Australia."