And for an animal but non-mammal example, there are penguins.

Sea snakes, as well.

And sea turtles, and I guess iguanas are a kind of sea lizard.

> iguanas are a kind of sea lizard

Only the marine iguanas, but yes.

Also salt-water crocodiles (the largest living reptile).

Mangroves are aquatic trees that evolved from regular land trees.

Sea grass is a monocot but belongs to a different order (Alismatales) than true grass (Poales).

Thanks for the correction. Interesting