- Frogs swallow with the assistance of their eyes. When eating, a frog will close its eyes and use its ocular muscles to shove food down its throat. A study from the University of Massachussetts Amherst in which eye muscle nerves were cut in northern leopard frogs found that the amphibians had to swallow about twice as much to get their meals down.
- A woodpecker’s tongue is so long that it wraps around the bird’s head and is stored in one nostril.
- Hagfish have no jaws, no eyes, and no bones, but they’ve survived for at least 300 million years because of their one defense. They ooze slime. While seemingly a really lame secret weapon, the mucus-like goo can clog fish gills and suffocate predators. Another fun fact about hagfish: they regularly tie themselves into knots.
- Moray eels have a second set of jaws, called pharyngeal jaws. When the eel extends its mouth, these jaws push outward like spiky tongs, then retract to pull prey down the eel’s throat. It’s believed these jaws developed from the same structure as oral jaws, the pharyngeal arches present in the ancestors of vertebrates.
- Cetaceans, e.g. whales and dolphins, as well as seals and birds, can sleep using half their brain. Known as “unihemispheric sleep,” (UHS) the phenomenon allows the animal to register potential threats and even keep moving while at least partially unconscious. In cetaceans, which unlike birds and seals rely almost entirely on UHS, the hemispheres take turns sleeping. The corresponding eye often closes, while the other eye may remain active.
- In a sentence that sounds like it belongs in a Daniel Pinkwater novel, planarian flatworms can “remember” experiences even after their heads have been chopped off. Planaria have a high ratio of pluripotent cells to differentiated cells, meaning they can regenerate almost any part of their body, including their brain. A 2013 experiment from Tufts University showed that planaria conditioned to accept bright light over the course of multiple trials did not revert to their natural state of avoiding light after their brains were chopped off and had regrown. This finding suggests that the information was stored outside of the brain, and may have implications for how the nervous system operates.*
- Possibly the strangest example of metamorphosis takes place in the starfish Luidia sarsii. The animal begins life as a larva. When the adult stage has developed sufficiently inside the larva, it detaches and starts life as a starfish. Meanwhile, the larva continues to live independently. This and other examples of odd echinoderm transformations inspired the theory that these animals evolved from two completely different lineages, only appeared because sperm from one ancestor accidentally fertilized an egg from the other.
- A frog’s tongue is backwards from a human tongue in that it attaches to the front of the mouth instead of the back. This reversal allows the frog to fling its tongue, which can be between a third and a half of the frog’s body length, at unsuspecting prey.
- A flamingo’s beak is upside down compared to other birds. In most birds, the upper beak half is larger and the lower half is mobile. In the flamingo these traits are reversed. A widely accepted explanation for this inconsistency is that flamingoes feed with their heads upside down. They stir up sediment (and prey) with their feet, then swing their heads into the water with the top of their head facing down. The flamingo beak is also specialized for straining out small creatures.
- Ferns may launch their spores by loading them into a natural catapult. The catapult is a ring of specialized cells, called an annulus, that unfurls into a line then releases tension to fling the spores. It’s believed that this mechanism helps spread fern offspring as far from the parent as possible, though the flung spores still have to be lucky enough to land on fertile ground.
*Side note, if Wolverine could regenerate like a planarian then the events of the first few X-Men films may have been very different.