Cuttlefish

Pfeffer's Flamboyant cuttlefish is poisonous, little larger than a golfball, and is found along the barren underwater plains of the Indo-pacific.  While we can see that it is an interesting creature, as far as sealife goes it first appears relatively standard in its weirdness.  What is most unexpected about the flamboyant cuttlefish, though, is found in the way it gets around.  Over millions of years it has lost most of its ability to swim about like its cephalopod relatives the squid and nautilus, instead it trudges across the sea floor, pulling itself along using four areas of its fluttery fin .  This gives it an extraordinary resemblance with a four-legged land animal, and is very curious to see on the ocean floor.

http://video.yahoo.com/watch/1605753/5417924