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Technicians at the Museum of New Zealand today started defrosting a rare colossal squid for a scientific examination on Wednesday.

They first removed the specimen - caught in February 2007 in Antarctic waters - from the freezer on Sunday, but realised it would thaw quicker than expected because it was encased in relatively little ice.

It was taken out again this afternoon. A tonne of ice was added to its bath of salt water, but late today the thawing was still too rapid and more ice will be added tomorrow.

The thawing has to be carefully controlled because if gets too warm, the outside could rot while the inside remains frozen.

Staff have separately thawed a giant squid and a damaged specimen of a colossal squid - each weighing about 200kg - and several juvenile colossal squid to work on in the run-up to Wednesday's presentation of the colossal squid, which weighs 495kg.

The work on the smaller specimens tomorrow will also be broadcast on the internet.

First named in 1925 from the base of two tentacles found in a sperm whale's stomach, the colossal squid has only rarely been sighted since then - mostly through partly dismembered, digested or rotted body parts recovered from whales, or washed up on beaches.

Auckland squid expert Steve O'Shea told the website for octopus and squid enthusiasts that the first thing his team will do with the thawed squid is measure the "beak" it uses to cut it food into tiny pieces.

The largest beak so far recovered is 49mm long, but the immature female Dr O'Shea dissected in 2003 had a beak 38mm long and a mantle (body) length of 2.5m.

The next step will be to determine the sex of the squid. This one is thought likely to be a male about 8m long, but females usually grow bigger than males.

He will check its reproductive systems to determine maturity, and the gut, including stomach contents. An endoscope may be pushed down the squid's oesophagus and up its intestine.

The species appears to be a fearsome predator, with unique swivelling hooks on the club-like ends of its tentacles. It was caught by a toothfish longliner, clamped onto a toothfish hauled up to the surface.

On Thursday, the scientists will give public lectures about their initial results.

Once thawed and examined, the squid will be "fixed" by being injected with bicarbonate of soda mixed with formalin, and soaked in 7000 litres of formalin to be preserved.