In my Bio II class, we're working our way through the various classifications of life. We started off with the prokaryotes. They were all right. Talking about all the nasty ways viruses and bacteria can destroy you was great fun for the students.
Next up is "protists". And I gotta ask...
What the hell were you guys thinking on the classification on this one?!
The definition is a pure anti-definition: It's everything eukaryotic except plants, animal, and fungi. That only leaves (according to one source) about 30,000 species left to classify into some kinda sub-groups. So how do you do it?
I have no damn clue. Why? Because I've seen no less than five different methodologies for doing so. Miller and Levine uses one. Wikipedia uses a different. John Kimball (the author of another Biology textbook) uses yet another!
Yes, I get that the classification is a messy business and these little buggers go so many different ways that it's a nightmare for you, but trying to teach this in any logical, digestible manner is impossible. Every classification scheme has exceptions in every category. I try to define something only to find a list of counter-examples!
Someone let me know when protists make sense. Until then, my students will get another fun section of memorizing all the ways protists can do whatever it is each one does with no sane categorization to tie it all together.