Sure you know Poliwags are meant to be tadpoles (and if you didn't...you probably have time to think about things other than what Pokemon are based on. Good for you). But the weird thing about Poliwag is a certain design choice that most wouldn't think has any significance. The swirl on Poliwag's (as well as Poliwhirl and Poliwrath's) stomach isn't just an aesthetic design - it's based on some species of translucent tadpoles' visible, swirled intestines.
2. Gorebyss is the long-nosed chimaera
Gorebyss very closely resembles the long-nosed chimaera - particularly in the face: they both share the innocent, cutesy eyes and the long snout. Except, of course, Gorebyss looks pretty ridiculously cute and has Ariel-esque shells permanently attached to it, and the long-nosed chimaera is a creature from your nightmares made real.
3. Caterpie is based on the Eastern tiger swallowtail caterpillar
Sure, Caterpies are based on caterpillars - but the specific design of Caterpie (including its weird attenae things) ARE based on a specific kind of caterpillar. Even more weirdly - that thing you thought was Caterpie's eye? NOPE. Just a marking on the caterpillar. Are Caterpies totally blind? Not saying definitively, but mine has missed A LOT of String Shots.
4. Luvdisc is based on the kissing gourami
Luvdisc instantly looksl ike such a silly fish - its pink coloration, heart-shape, and...does it actually have lips?! Why would a fish have lips? For kissing or someth...oh. The kissing gourami even ACTUALLY kiss (sorta) - they lock "lips" to spar with one another.