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.
By Laura Klappenbach. 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).ea urchins have tube feet and move using a water vascular system. Their endoskeleton consists of calcium carbonate spicules or ossicles. In sea urchins, these ossicles are fused into plates that form a shell-like structure called a test.