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Squid eyes under the knife Jun 11 2008

What has eyes the size of dinner plates, fearsome suckers that cling to its prey, razor-sharp hooks to shred its victims and two beaks to crush the remains?  It’s the colossal squid (Mesonychoteuthis hamiltoni) – an elusive “killing machine” from the dark depths of Antarctic seas.

A recent dissection has shown these squids to have the biggest eyes ever recorded in the animal kingdom.  Read the full BBC report here. 

“In the collapsed state we see here, they [the eyes] measure 25cm [almost 10in] across, but in the living animal they are probably larger, up to around 30cm [close to 12in],” said Professor Eric Warrant, an expert on animal vision at the Museum of New Zealand Te Papa in Wellington. The pupils alone are about 8cm (3in) across.

The giant eyes are thought to help the fearsome species locate prey in the dark Southern Ocean depths.

The 10m-long (34ft) specimen caught, weighing in at about 495kg (half a ton), has also turned out to be female, surprising the scientific team, which initially thought the catch was male. This sheds new light on how big the creatures can grow. Females are thought to be larger – so if this had been a 10m male, one would assume there were far bigger specimens lurking in the ocean depths.

Very little is known about colossal squid – only about 10 have ever been caught and brought to shore – but the creature’s reputation has been entangled in sea lore since the 1700s. An alleged encounter between a ferocious, man-eating squid and a French naval vessel was vividly described in Jules Verne’s book Twenty Thousand Leagues Under the Sea, which was published in 1870.

Scientists hope the latest dissection will yield new information about where and how colossal squid live and breed.

The find has also enabled researchers to study the colossal squid’s swivelling barbed clubs at the end of its tentacles. “It’s endowed with a killer arsenal: the hooks, the beak, everything about it,” said Steve O’Shea of the University of Technology in Auckland, New Zealand. 

Large squid and sperm whales have been known to engage in lethal battle – evidenced by the scars, caused by the squid’s serrated hooks, found on the heads of sperm whales.

But Professor Paul Rodhouse, head of biological sciences at the British Antarctic Survey, is more concerned about the future of the colossal squid than the fate of creatures that may encounter one. He is particularly worried about the recent flood of fishing vessels into Antarctic waters targeting Patagonian toothfish (Dissostichus eleginoides), which is a major prey species for colossal squid.

“Toothfish and these squid form part of a deepwater ecosystem that we know virtually nothing about, yet are already exploiting it through commercial fishing,” Rodhouse added.

At least the colossal squid isn’t likely to join toothfish on the seafood menu. Calamari as big as car tyres might sound tasty, but jumbo-sized squid usually contain high levels of ammonia and their meat is said to taste like floor cleaner!

Images of squid eye lens and dissection courtesy Museum of New Zealand Te Papa Tongarewa.

References:

Black, R 2008, ‘Colossal squid’s big eye revealed’, BBC News. Retrieved 6 May, 2008, from http://news.bbc.co.uk/1/hi/sci/tech/7374297.stm

Owen, J 2003, ‘Colossal squid revives legends of sea monsters’, National Geographic News. Retrieved 13 May, 2008, from http://news.nationalgeographic.com/news/2003/04/0423_030423_seamonsters.html.

Shears, R 2003, ‘Colossus of the deep’, Daily Mail, London. Retrieved 13 May, 2008, from http://www.bio.net/bionet/mm/deepsea/2003-April/000588.html.