I just came up with this on the fly while in my 5th grade class today. We've already talked about classification and are now talking about invertebrates and vertebrates. I just thought of Classifying Spongebob! Basically we take all the characters from spongebob and the kids have to decide if they are vertebrates or invertebrates, then what sub-category- mammal, fish, echinoderm, mollusk, etc. It's great because they know the characters and basically all of the categories are covered!!
I'm trying to think of maybe a longer more extended activity, but for now the kids had a great time classifying spongebob