By Richard Black
Environment correspondent, BBC News website

The huge eye of the world's largest squid has been revealed by scientists dissecting a rare, intact half-tonne specimen in New Zealand.

About 27cm (11in) across, researchers believe the colossal squid's eye is the biggest animal eye ever found. The 10m-long (34ft) specimen has also turned out to be female, surprising the scientific team. Very little is known about colossal squid; only about 10 have ever been caught and brought to shore. This one was caught by fishermen in the Ross Sea near Antarctica last year.

Scientists hope the dissection will yield new information about where and how colossal squid (Mesonychoteuthis hamiltoni) live and breed.

"These are truly amazing eyes," commented Eric Warrant from the University of Lund in Sweden, an expert on animal vision who is at the Museum of New Zealand Te Papa in Wellington to take part in the dissection.

"In the collapsed state we see here, they measure 25cm across; but in the living animal they are probably larger, up to around 30 cm." With a diameter larger than a football, these would help the fearsome hunters locate prey in the dark Southern Ocean depths. The pupils alone are about 8cm (3in) across

"These are without doubt the largest eyes that have ever been studied, and probably among the largest eyes that have existed during the history of the animal kingdom," Professor Warrant concluded.

Hooked on food

The 10-strong team of researchers had initially believed the colossal squid to be male. Instead, they found ovaries containing thousands of eggs. This may have implications for understanding how big the creatures can grow.

Females are thought to be larger; so if this had been a 10-metre male, it would have been logical to assume there were much bigger specimens out there. The creature's lower beak has also emerged, and measures about 4cm across.

Scientists have also been able to examine in more detail the swivelling barbed clubs at the end of its tentacles.

"It's endowed with a killer arsenal: the hooks, the beak, everything about it," observed Steve O'Shea from the University of Technology in Auckland. A endoscope has been inserted down into the animal's stomach in the hope of identifying what it had been eating before it was caught.

The team is also dissecting a much smaller colossal squid specimen that has part of its body missing, and a giant squid - a member of the Architeuthis genus. Architeuthis can be as long as colossal squid, but their bodies are smaller and thinner. Neither of these marine monsters is frequently seen, but Mesonychoteuthis is especially elusive. Later in the week, the team is expected to give public lectures about the initial results. Once thawed and examined, the squid will be embalmed and preserved.