There are two. The first is your endless supply of rocks, which you throw like a little schoolgirl, and the other is a slingshot. However, you really don't get the slingshot all that much, so when you eventually get to use it, you are so accustomed to the rocks that you miss half of the enemies you're trying to hit. This is just a theory. There are actually quite a few.
Lets get right to the pirates.
Another interesting opponent was the squid, as they fire two different projectiles - a blue ball and a black ball. At first the black ball will render your character blue, and then you must then be hit with a blue ball to return to your original state. Originally the blue ball will kill you, and if you're hit with a blue and then black ball, you will be killed as well. It's best not to think about this too much. Avoid all squid balls of any color at all costs, even the red ones.