Polymastia echinus is a species of demosponge

Demosponge

The Demospongiae are the largest class in the phylum Porifera. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges...

 belonging to the family Polymastiidae

Polymastiidae

Polymastiidae is a family of demosponges found in oceans throughout the world. A useful diagnostic characteristic of members of this family is the presence of numerous surface papillae although this feature is shown by some other sponges.-References:*...

. It is only known from shallow subtidal habitats off Goat Island

Goat Island, New Zealand

Goat Island, New Zealand may refer to any of three islands:*Goat Island, Auckland*Goat Island, Otago Harbour*Goat Island/Te Mapoutahi, also in Otago...

 in the far north of the North Island

North Island

The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...

 of New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

.

This is an encrusting sponge with an extraordinary appearance. The sponge is always largely covered in sand, grit and fragments of shells apart from smooth, cylindrical, peach-coloured papillae up to 15 mm in height which are always free of such material. The specific name refers to this rather hedgehog

Hedgehog

A hedgehog is any of the spiny mammals of the subfamily Erinaceinae and the order Erinaceomorpha. There are 17 species of hedgehog in five genera, found through parts of Europe, Asia, Africa, and New Zealand . There are no hedgehogs native to Australia, and no living species native to the Americas...

-like appearance.