Pleco identification: common or bristlenose?

I have two plecos. I took them home from my high school biology room. I always assumed they were common, but now I am not too sure. They are the same size, but one has bright yellow spots on its head (the rest of its spots are white) and very stubby, short bristles. The other has no bristles whatsoever and all of its spots are completely white. My biology teacher had told me the difference in bristles was a sexual dimorphism (males have bristles, females have none), but I'm not so sure after looking at profiles for common and bristlenose plecos. Any pictures I've tried to take of either fish have been terrible. This common pleco looks almost identical to my "female":



Again, the "male" pleco's head spots are crayola yellow, and it has short bristles that only emerge from the edge of the lip.

My best guess is that the "female" is a common pleco and the "male" is actually a female bristlenose pleco. Any more educated guesses?

 

Welcome to Fishlore, Nudibranch.

I've moved your post out of the plant profile section of the forum and into the pleco section.
Unfortunately, I know nothing about sexing plecos, so I can't help you with that. We do have many pleco keepers, and at least a couple who have bred them. Perhaps someone will be able to help.

 

looks like a bristlenoise to me

 

It's hard to tell without a picture, but here's a picture of my female bristlenose. It's not the clearest picture, but maybe it will help.

 

Gold nugget pleco?

EDIT: nevermind, googled it, not that.

 

Question, do they have any light bands/stripes on any of their fins?

 

Looks to me like a common Bristlenose Pleco. And yes males have the bristles while they female doesn't.