There are arguments against Ursula saying if she is an actual Octopus-thing or not. Many people don't think she is an octopus-thing because she has only six tentacles instead of eight, like every octopus should have. However, others rebuke this argument claiming that her two arms stand in place of the two tentacles. 

But what most people don't know is that the reason Ursula only has six tentacles is because it was cheaper to animate her with six tentacles rather than eight.