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.
Figure A shows the aboral (opposite of mouth) view of a sea urchin test (shell). The center of the test shows the anus (very center), the 5 gonopores (5 black dots near the points of the pentagon) and madreporite (single oval in top section of pentagon).ea urchins are unsegmented and penta-radial as adults. From fertilization to just before metamorphosis, the young sea urchin is bisymetrical (as are humans). At metamorphosis, the sea urchin takes on the characteristic five sided penta-radial design.