Rays and skates are members of a superorder of fishes called Batoidia (they're also in the subclass Elasmonbranchii, to which sharks also belong). Batoids are super weird. You should read about them. But for the purposes of this comic, what you need to know is that batoid undersides look like funny little faces.
In other news, I've just discovered the tumblr of comic artist, children's book author & Simpsons animator Liz Climo, and it might be the most charming thing I've ever seen. Here's another of her webcomics. It's also elasmobranch-themed (because goblin shark):
See? Delightful as hell. Much more here.
H/t David Shiffman