Did you get to play with these guys in biology class?
I remember in high school we got some planarians to mess around with... if you cut them in half they'll grow into two worms, and if you cut the head in half it'll grow two heads.
They are flatworms, phylum Platyhelminthes.
I made a few plushies! One small, one medium, and one with two heads. Available now in my etsy shop.