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.
Sea urchins are Echinoderms, spiny-skinned animals related to starfish and sea cucumbers. Echinodermata is a rather small phyla of animals and is unique in that virtually all members of this group are strictly marine. They also, as a group, employ nearly every type of feeding method exhibited by animals.