What is "lyngbakr"

Lyngbakr ( Icelandic, lyngi " heather" + bak "back") is the name of a massive whale-like sea monster reported in the Örvar-Odds saga to have existed in the Greenland Sea. According to the saga, Lyngbakr would bait seafarers by posing as a heather-covered island, and when a crew landed on his back, he sank into the sea, drowning the crew.