I love Ortelius' Islandia map which uses those sea monsters. I especially enjoy the description of the monster standing straight up that reads (translated):
Staukul -- The Dutch call it Springual. It has been observed to stand for a whole day long upright on its tail. It derives its name from its leaping or skipping. It is a very dangerous enemy of seamen and fishermen, and greedily goes after human flesh.
The Ortelius map is indeed a masterpiece; a great inspiritian for any kind of old-style map. Luckily there exist high-quality scans of this map.