A worm’s head is located at the end of the worm closest to the part of the body called the clitellum. Worms travel head first, extending their heads when crawling. It’s easy to determine where a worm's head is by observing it in motion.
Worms use a complex system of muscles that enable them to move and wiggle. They do not have eyes, but rather receptor cells that are touch- and light-sensitive. They can feel underground vibrations using these cells.
Earthworms have brains that are simple and that specialize in helping to direct the worm’s body. Worms do not have lungs, but breathe through their skin, necessitating that their environment be continually moist. If a worm’s skin becomes dried out, it dies of suffocation.
There are nearly 4,400 types of worms, as of 2015, 2,700 of which are different types of earthworms and more than 1,200 species that are inch worms.