--- title: The Arctic Ocean: walruses, bowheads, the 400-year shark and the unicorn's tooth — a lesson of Mova's school · trees and pragmatics description: «The Arctic Ocean: walruses, bowheads, the 400-year shark and the unicorn's tooth», a lesson of the biology course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: The Arctic Ocean lies around the North Pole under a lid of floating sea ice that grows in --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/) / The Arctic Ocean: walruses, bowheads,… # The Arctic Ocean: walruses, bowheads, the 400-year shark and the unicorn's tooth Lesson 169 of the biology course of Mova's primary school: 16 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/0/) — The Arctic Ocean lies around the North Pole under a lid of floating sea ice that grows in winter and shrinks in summer, and the animals there live on, under and around that lid. - [1](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/1/) — A walrus climbing out onto the ice is like you hauling yourself out of a swimming pool with two ice picks: it hooks its long tusks into the ice and drags its heavy body up. - [2](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/2/) — Under the ice swim some of the oldest animals on Earth: bowhead whales that may live over two hundred years and Greenland sharks that may live about four hundred, so a shark alive today could have been born before your great-great-great-great-grandparents. - [3](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/3/) — Long ago traders sold narwhal tusks in Europe as unicorn horns; the tusk is really a long spiral tooth, and as the world warms the sea ice is shrinking, making life harder for polar bears and seals. - [4](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/4/) — A walrus has two long tusks, and walruses use their tusks like ice picks to pull their heavy bodies out of the water onto the ice. - [5](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/5/) — Walruses find clams on the dark seabed with hundreds of sensitive whiskers and suck them out of their shells. - [6](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/6/) — Bowhead whales can smash through ice with their heads to make breathing holes, and they may live for over two hundred years; old harpoon tips from the 1800s have been found in living whales. - [7](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/7/) — The Greenland shark is the longest-lived animal with a backbone known, perhaps living about four hundred years, and scientists measured its age using a kind of carbon clock in the lens of its eye. - [8](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/8/) — Belugas are white whales called sea canaries because they whistle, click and chirp, and a beluga can change the shape of its forehead, called the melon, to aim its clicks. - [9](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/9/) — Polar bears hunt seals by waiting at breathing holes for hours or even days. - [10](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/10/) — Polar bear skin is black and its fur is made of see-through hollow hairs that look white because they scatter light. - [11](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/11/) — Ringed seals dig snow caves on the ice to hide their pups and keep breathing holes open by scratching the ice with strong claws. - [12](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/12/) — Arctic sea ice is shrinking because the world is getting warmer, and some polar bears now have to swim much longer distances, sometimes for days. - [14](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/14/) — Harp seal pups are born white on the ice, turn grey after a few weeks, and grow very fast on milk that is about half fat, building a thick layer of fat called blubber before they must swim in icy water. - [15](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/15/) — In the Middle Ages narwhal tusks were sold in Europe as unicorn horns; a narwhal's tusk is a tooth that grows out through its lip in a spiral, mostly in males. - [16](https://md.mova.elamur.ai/free/en/corpora/school/biology/169-the-arctic-ocean-walruses-bowheads-the-400-year-shark-and-the-unicorns-tooth/16/) — The arctic tern makes the longest migration of any animal, flying from the Arctic to Antarctica and back each year, and in a lifetime it may fly as far as to the Moon and back several times. - ← previous: [The Arctic tundra: musk oxen, arctic foxes, snowy owls and the truth about lemmings](https://md.mova.elamur.ai/free/en/corpora/school/biology/168-the-arctic-tundra-musk-oxen-arctic-foxes-and-the-truth-about-lemmings/) - next →: [Antarctica: emperor huddles, krill, clear-blooded fish and stone-stealing penguins](https://md.mova.elamur.ai/free/en/corpora/school/biology/170-antarctica-emperor-huddles-krill-clear-blooded-fish-and-stone-stealing-penguins/) - ↑ back to [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/)