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Is a newly discovered sandhopper the biggest freeloader in the ocean or is it a better guest than the fish that hides inside a sea cucumber?
Niwa marine biologist Dr Dennis Gordon, of Wellington, has discovered a new species of sandhopper.
He believes the female sandhopper makes a slit in the backside of another deep-sea organism - a bryozoan species that lives deep in the Chatham Rise, in the Pacific Ocean east of the South Island - and enters with a dwarf male, to breed and live inside the host with its family.
The slit on the host repairs and the hoppers live inside until the host dies. The hoppers then leave to colonise another bryozoa.
The hoppers are up to 1cm long and have been discovered living inside bryozoa up to 5cm long.
Dr Gordon was unsure if the hoppers living protected in a transparent membrane cavity of the host were a welcome guest or unwanted.
The hoppers and the bryozoa could benefit or the hoppers could be the sole beneficiaries, taking nutrients and protection from their host, Dr Gordon said.
''We are also wondering if there is a two-way nutrient flow whereby the secretions of the hopper can be transferred to the bryozoan, but we don't really know.''
To reveal more on the relationship, live specimens needed to be collected, which was difficult when they lived at a depth of between 500m and 1500m.
Dr Gordon said many animals had unusual relationships, including a fish that lived in the rectum of a sea cucumber in the Caribbean.
The fish used the rectum to shelter from its enemies, he said.
''It doesn't bother the sea cucumber but I don't think it gains anything either.''
The new sandhopper was called Bryoconversor tutus.
More samples of the sandhoppers would be collected for further DNA testing, Dr Gordon said.