The sea monk is found in some medieval encyclopedias. Its lower body is shaped like a fish, but its upper body looks like a human. Its head resembles that of a freshly shaved monk, with the top of the head shaved and white, and a black circle around it above the ears, like the tonsure of a monk. It likes to play near shore to attract people with its games, but when someone gets close enough, the fish pulls them into the water and eats them.

The sea monk was described in several sixteenth century natural histories (e.g. Conrad Gessner, Historia animalium, 1551 CE) as being a real animal. One was reported to have been captured in the sea between Denmark and Sweden in the 1540s. It has been identified as the giant squid and the angelshark.