Colossal squid

The colossal squid was first described in 1925 by British zoologist Guy Coburn Robson, who named it Mesonychoteuthis hamiltoni after a specimen recovered from a sperm whale stomach.¹ For decades it was known only from beaks and partial remains found in whale stomachs, leading to confusion with the giant squid (Architeuthis dux).² The first intact specimen, a juvenile female, was captured in 2003 by a New Zealand fishing vessel in the Ross Sea.³ A larger adult, 8.5 m long and weighing 495 kg, was caught in 2007 and is now preserved at the Museum of New Zealand Te Papa Tongarewa.⁴

The colossal squid possesses the largest eyes of any known animal, reaching up to 27 cm in diameter, which allow it to detect faint bioluminescent prey in the dark depths.⁵ Unlike the giant squid, its tentacles are armed with sharp, swiveling hooks in addition to suckers, a unique adaptation for grasping large prey.¹ Its mantle is heavy and muscular, and it contains high concentrations of ammonium chloride for buoyancy, a trait shared with other deep-sea squids.⁶ The beak is the largest of any squid, and its size is used to estimate body mass from whale stomach contents.²

The colossal squid is an ambush predator that hunts large fish, such as the Patagonian toothfish, and other squids in the mesopelagic and bathypelagic zones down to 2,200 m. It is a major prey item of sperm whales, which dive to these depths to feed, and its beaks are commonly found in whale stomachs.² The species exhibits sexual dimorphism, with females growing larger than males, and it is thought to have a slow metabolism and a lifespan of several years.⁶ Its population is not well quantified, but it is not considered threatened, though climate change and deep-sea fishing may impact its habitat.

The colossal squid's eye is not only large but also lacks a lens in some preserved specimens, leading to speculation about its visual capabilities; it may rely on detecting large silhouettes rather than fine detail.⁵ The species was once mistakenly classified under the genus Architeuthis due to incomplete remains.¹ Its hooks are so sharp that they have been known to injure researchers handling frozen specimens.⁴ The 2007 specimen was caught after it had been feeding on a toothfish caught on a longline, suggesting it may scavenge as well as hunt.³ The colossal squid's beak is so hard that it can survive digestion, providing a record of its distribution from whale stomach contents.²

Mantle

The main body mass of a squid, containing the internal organs.

Beak

The hard, parrot-like mouthpart of a cephalopod, used for biting prey.

Mesopelagic zone

The ocean layer between 200 and 1,000 meters depth, where little light penetrates.