Buizel and Floatzel
Members of the "pokemon I constantly forget exist" department, this line at least has an interesting idea behind it. They're "weasels," but adapted for an aquatic lifestyle, with organic "floats" around their necks, little fins on their arms, and split tails that propel them through the water.
Of course, the real world already has aquatic mustelids that we call "otters," but I get the distinct sense that these are not otter pokemon. These really are weasels that evolved to live like otters, in the same way shrews and moles are two different things in the same group but there are in fact both "mole shrews" and "shrew moles." Look them up. There are also water shrews and water moles! Water moles are called "desmans!"
Alrighty! Did you look up desmans yet??