Seals. A female, white seal with sparkly eyes and a smiling face would be so cute, and a male, black and grey seal with a mysterious smile would be a great cranky in my opinion. One day I'll post a drawing of them.
LOL at everyone suggesting animals only slightly different from existing animals. Technically we already have parrots as they are a common variation of the eagle species in the game. If they were to introduce an actual parrot species it'd be a waste, there's already so many birds and so few other classes.
Now then, we really need another reptile group. Alligators are the sole representative and they're not as appealing to me as they should be. I feel like a lizard species would be incredibly cool to see.
Sharks and/or dolphins is an obvious choice, because there's nothing like them in the game right now and they're a very popular animal type. I've seen fanart of them and they look fantastic.
Sharks and Dolphins sound neat (How does that work with fishing and air?). On the same note, I think jellyfish are super cute and would make a nice addition. I've always wanted to see more hedgehogs in the game as well as llamas.