IELTS Online Practice Materials

Colossal Squid

(A) The colossal squid (Mesonychoteuthis hamiltoni, from Greek mesos (middle), onycho (claw, nail), and teuthis (squid)), sometimes called the Antarctic or giant cranch squid, is believed to be the largest squid species in terms of mass. It is the only known member of the genus Mesonychoteuthis. It is known from only a few specimens, and current estimates put its maximum size at 12–14 metres long and weighing possibly up to 750 kg, based on analysis of smaller and immature specimens, making it the largest known invertebrate.

(B) Unlike the giant squid, whose arms and tentacles have only suckers lined with small teeth, the colossal squid's limbs are also equipped with sharp hooks: some swivelling, others three-pointed. Its body is wider and stouter, and therefore heavier, than that of the giant squid. Colossal squid are believed to have longer mantles than the giant squid, but shorter tentacles.

(C) The squid exhibits abyssal gigantism. The beak of the colossal squid is the largest known of any squid, and more robust than that of the giant squid. The colossal squid also has the largest eyes documented in the animal kingdom; a partly collapsed specimen had eyes measuring 27 cm in diameter, with a 9 cm pupil. The eye was estimated to be 30 to 40 cm when the squid was alive.

(D) The squid's known range extends thousands of kilometres northward from Antarctica to southern South America, southern South Africa, and the southern tip of New Zealand, making it primarily an inhabitant of the entire Southern Ocean.

(E) Little is known about the life of this creature, but it is believed to feed on prey such as arrow worms, large fish such as the Patagonian toothfish, and other squid in the deep ocean using bioluminescence. A recent study revealed that Antarctic toothfish make up a significant part of the colossal squid's diet; of the 8,000 toothfishes brought aboard trawlers between 2011 and 2014, 71% showed clear signs of attack by colossal squid. The colossal squid is thought to have a slow metabolic rate, needing only around 30 grams of prey daily. Estimates of its energy demands suggest it is a slow-moving ambush predator, using its large eyes primarily for predator detection rather than active hunting.

(F) Based on capture depths of a few specimens, and beaks found in sperm whale stomachs, the adult colossal squid ranges at least to a depth of 2.2 km, although juveniles can only go as deep as 1 km. It is believed to be sexually dimorphic, with mature females generally being much larger than mature males, as is common in many species of invertebrates.

(G) The squid's method of reproduction has not been observed, although some data on their reproduction can be inferred from anatomy. Since males lack an organ called a hectocotylus (an arm used in other cephalopods to transfer a sperm to the female), they probably use a penis instead, which would be used to directly implant sperm into females.

(H) Many sperm whales have scars on their backs, believed to be caused by the hooks of colossal squid. Colossal squid are a major prey item for sperm whales in the Antarctic; 14% of the squid beaks found in the stomachs of these sperm whales are those of the colossal squid, which indicates that colossal squid make up 77% of the biomass consumed by these whales. Many other animals also feed on colossal squid, including beaked whales (such as the southern bottlenose whale), pilot whales, southern elephant seals, Patagonian toothfish, sleeper sharks, and albatrosses (e.g., the wandering and sooty albatrosses). However, beaks from mature adults have only been recovered from large predators (i.e. sperm whales and sleeper sharks), while the other predators only eat juveniles or young adults.

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Adapted from Wikipedia