This one is not so exciting to look at, but it totally wins the bizarre animal contest. It is colloquially known as a “sea squirt.” This is a sea critter that eats its own brain. A marine invertebrate, it spends part of its life in a larval stage where it can swim around in the water much like a fish or any other mobile animal. This is a relatively brief period in the sea squirt’s life. They cannot feed in this stage, so they swim off, find a nice little bit of seabed to settle in on, and then plant themselves.
Once there, they start feeding. They also begin absorbing their mobility features and gills. The eyes and notochord (like a spine) go next. Finally, the brain is absorbed. Having no need to move about anymore, all of these body parts are considered superfluous by nature and dispensed with (an intriguing indicator that eyes and brains are necessarily mainly for reasons of mobility and are unnecessary for stationary organisms like plants—no wonder many of us feel an urge to travel). The material is then recycled to create whole new body systems, including digestive, reproductive, and circulatory systems. Then the hermaphroditic tunicate reproduces, expelling brand new sea squirts into the world. It doesn’t get much more alien than that.