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.
Definition of mushroom. 1  1a : an enlarged complex aboveground fleshy fruiting body of a fungus (as a basidiomycete) that consists typically of a stem bearing a pileus; especially : one that is edibleb : fungus. 2  2 : upstart. 3  3 : something resembling a mushroom.