Seven new species of sea urchins known as tam o'shanters have been discovered in a collection of urchins in the National Institute of Water and Atmospheric Research's (NIWA) Invertebrate Collection.

Deep water fisheries scientist Owen Anderson says unfortunately people have little chance of seeing any of the new species alive because they live so deep in the ocean.

The giant urchin Araeosoma alternatum grows up to 23 cm in diameter. Photo: Owen Anderson.

Deep sea urchins are widespread but are most commonly found off the Bay of Plenty, on the Chatham Rise, and on the Campbell Plateau.

Owen says they are not found on beaches and are too deep for divers to see, so to find one is incredibly rare. They are occasionally seen when caught in deep sea nets.

'These urchins live at a depth of 100-1200 metres and are named tam o'shanters as their shape is similar to a Scottish hat.

'New Zealand waters are rich with diversity when it comes to this urchin group - there are about 50 known species in the world with nearly a third of these found in New Zealand waters.”

These deep sea urchins don't have a hard shell like their cousin kina and the various tropical species that can be seen in less than 10 metres of water, instead the tam o'shanters have a flexible leathery outer skin adapted for the deep sea environment in which they live.

'There are many different kinds of urchins, which I hadn't appreciated before I started researching kina but now I am hooked.

'I love the symmetry and detail of the shell plating, they are very beautiful. I had the privilege of naming the seven new species and I'm also in the process of researching, identifying, and describing a further seven species.”

These deep sea urchins are frequently found around mountainous underwater areas called seamounts and NIWA's research on these features revealed a particular hotspot for tam o'shanters in the seamounts of the Bay of Plenty where nine separate species have been found.

Owen says this research resolves confusion around the tam o'shanter species Araeosoma coriaceum, supposedly recorded off northern New Zealand by the Challenger Expedition in 1874 and again recorded 100 years later in the Hauraki Gulf.

Examination of old specimens, new material, and original descriptions led to the conclusion that the Challenger specimen had been mislabelled with its true locality unknown. The Hauraki Gulf specimen therefore had been misidentified, it was not Araeosoma coriaceum, but a new species now known as A. bakeri.

This group also includes the giant Araeosoma alternatum, which grows up to 23 cm in diameter. Mr Anderson says that this species was only known from a single specimen, found in the Indian Ocean near Somalia in 1899, and then stored in the Berlin Museum where it was destroyed in World War 2.

The good news is that this species was rediscovered alive and well, relatively rare but widespread around New Zealand, also in Tasmania and around Madagascar.

NIWA has a large collection of urchins that have been preserved and stored since the 60s with some remaining unidentified.

In New Zealand there are 100 different species known so far.

There are some tam o'shanters on display next to the giant squid at Te Papa museum in Wellington.