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.
Now, in CONTRAST.... Sand dollars are members of a specialized sub-group of sea urchins that are often referred to as the Irregular Urchins. These urchins differ quite a bit from the so-called Regular urchins because they show a suite of adaptations to living in sandy/muddy/ bottoms! In irregular sea urchins..ow, in CONTRAST.... Sand dollars are members of a specialized sub-group of sea urchins that are often referred to as the Irregular Urchins. These urchins differ quite a bit from the so-called Regular urchins because they show a suite of adaptations to living in sandy/muddy/ bottoms! In irregular sea urchins..