The kylok is found in some medieval encyclopedias. It is a fish that clings to rocks and senses when something approaches it. If it can, it eats what passes, but if it is something threatening, it contracts its body and clings more strongly to the stone. There are two kinds, one which can be eaten and one that cannot. It is hunted by people in the winter and preserved with salt for the summer.

Thomas of Cantimpré based his description of the kyloc on Aristotle (see Sources), but re-arranged and modified the text.

The kylok may be the sea anemone, which attaches itself to a solid surface and filter-feeds on anything that passes through its tentacles; or it may be the sea sponge, which also attaches to rocks (the thethya mentioned by Aristotle is a genus of sponges).