In brief: The mystery of the tam o’shanter

The discovery of seven new species of sea urchins, known as tam o'shanters, has helped resolve more than a hundred years of confusion about their distribution in New Zealand waters. The discovery was found in a collection of preserved samples of urchins in NIWA's Invertebrate Collection.

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Araeosoma coriaceum had previously been recorded off northern New Zealand by the Challenger Expedition in 1874 and again 100 years later by fishing trawlers in the Hauraki Gulf. But examination of old specimens, new material and original descriptions has led to the conclusion that the Challenger specimen had been mislabelled, with its true locality unknown.

The Hauraki Gulf specimen that followed had therefore been wrongly identified. It was not A. coriaceum, but a new species now known as A. bakeri.

Deepwater Fisheries Scientist Owen Anderson said research on where the species live revealed a particular hotspot for tam o'shanters in the seamounts of the Bay of Plenty where nine separate species have been found.

"These urchins live in very deep water – up to 1200 metres – and don't have a hard shell like other more familiar species, such as their cousin kina, that live in shallower waters. Instead, they have a flexible leathery outer skeleton – well adapted for the deepsea environment in which they live."

New Zealand waters are rich with diversity when it comes to this urchin group. There are about 50 known species of tam o'shanters in the world, with nearly a third of these found in New Zealand waters. They are named tam o'shanters because of their resemblance to a 19th-century Scottish cap. Keen followers of poetry will know that the tam o'shanter cap was named after the eponymous hero of the poem by Robert Burns.

Find out more about another tam o'shanter, Araeosoma thetidis, in the Collection's 'Critter of the Week' series