What to do about dolphins and whales?

[Wilphe]

(My first impulse was to make them Monstrous Humanoids, but that might be silly, because you'd expect something called "humanoid" to have arms and legs.)

Wel Dolphins are adaptated mammals so their fins are evolved* limbs anyway, so technically they do have arms and legs.

* This is assuming you aren't into Intelligent design**, in which case that's not really applicable.

** Intelligent design does apply in most D&D cosmplogies, along with it's close cousin "Intelligent-but-not-especially Wise design" for the more outre wizardly creations