A crocodile's sex is determined by the temperature, hot is a female, cold is male and a medium temperature can sometimes hatch a litter of hermaphrodites(so I'm told, don't hold me to that one).
Clown Fish change their gender depending on the amount of males or females present in the area at a certain age.
Sharks can throw up their own stomachs when frightened.
Some species of Sharks like the Sand Tiger(Grey Nurse to all you aussies) cannibalize one another in the womb.
Snakes and sharks do not have eyelids, but infact have something called a nictating membrane that slides over the eye in order to protect it.
One of the longest creatures in the world is a Sciphonophore, it lives in deep oceans and specimens up to 88 meters in length have been found. They are in fact a colony of jellyfiish-like organisms that form a much larger functional organism with a stomach, muscles and even primitive eyes.
In Sweden there's a forest of pine trees that all share the same root and has been disputed to be one of largest living organisms.