I saw an amigurumi version of this offered as a free pattern on Ravelry.

My first reaction: "Oh, no!" and laughter. (Planaria used to be a very common lab animal; they were used to study tissue regeneration because they have the funny little property of growing new parts when they're cut. In fact, some more devious experimenters would cut the head down the middle - I mean, down the medial line - and keep that cut open until it regenerated, and make two-headed planaria.)

My second reaction: "I kind of want to make one..."