Prominent among the family Ursidae is a polar bear that is adapted to a highly specialized semi-aquatic lifestyle. Although it is a bear yet it is listed as a marine mammal precisely due to the fact that it spends 50% of its life on ice floes and is able to swim as far as 90 km (60 miles).
urchin. 1  a mischievous boy. 2  any small boy or youngster. 3  sea urchin. 4  either of two small rollers covered with card clothing used in conjunction with the cylinder in carding. 5  Chiefly British Dialect. a hedgehog. 6  Obsolete. an elf or mischievous sprite.
When a sea star strives to get near an urchin, the urchin moves its spines aside and lets the sea star's arm get really close. Then the pincers chomp on the sea star's tube feet. The sea star immediately backs off. However, purple sea urchins' pincers can't defend against sunflower stars. If a sunflower star approaches, an urchin waves its spines and pincers and retreats. If the urchin doesn't move away fast enough, the sunflower star swallows the urchin whole.