>>40400815It's a natural progression.
Poliwhirl is scrawny and short, Poliwrath is taller and bulkier.
Poliwhirl's eyes rest atop its body, Poliwrath has grown to encompass its eyes.
Poliwhirl has mittens, Poliwrath has gloves.
Poliwhirl's chest spiral is in a circle, Poliwrath's chest circle resembles the tongue in a screaming mouth.