Origin: Medieval folklore
Sailors who land on remote islands best beware the Jasconius. The creature is enormous and its back appears as an inviting island where sailors may come ashore and rest. The Jasconius lies still until the crew has disembarked, when it suddenly submerges, dragging ship and crew to their watery graves. Other names for this beast are Fastitocalon, Zaratan or Aspidochelone.