A sea serpent by Michael Berenstain. The additional convolutions of its body are on the facing page, which I didn’t scan.
I’ve said this before, but I can’t get over it: Michael Berenstain is the son of the couple who wrote the Berenstain Bears books. The kid who was basically the basis for Brother Bear grew up to create The Creature Catalog. I just can’t get over that.
Holy shit, well, that’s pretty awesome.
Also, monster dude looks so much like the sea creatures illustrated in 15th century maps. Kinda funny how many of them have blow holes all over the place.