All Travel/Trivia

What is the given name of the titular figure in an Anglo-Saxon poem about a sea creature that can pretend to be an island in order to lure sailors to their doom?

Please send trivia responses in email with the subject line "trivia" directly to gabriel gryffyn (ggryffyn.cms@gmail.com). Previous weeks' trivia results will be announced en masse once a new prize has been decided on.