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 and sand dollars (Echinoidea) are a group of echinoderms that are spiny, globe or disk shaped animals. Sea urchins and sand dollars are found in all the world's oceans. Like most other echinoderms, they are pentaradially symmetrical (the have five sides arranged around a central point). Sea urchins range in size from as small as a couple of inches in diameter to over a foot in diameter. 1  They have a mouth located on their upper part of their body (also known as the oral surface) although some sea urchins have a mouth located towards one end (if their body shape is irregular).