Worms are invertebrates. There are actually several phyla of worms. They can live in a range of diverse environments. Some worms live in water, others on land, and some are parasites that live in the digestive systems of other animals! All worms lack legs. Flatworms are the simplest type of worm and have few organs, a head and a tail. Roundworms are slightly more complex than flatworms. They have simple digestive and nervous systems. Segmented worms are the most complex and include earthworms and fireworms. They have circulatory, nervous and digestive systems.

Ragworms are a species of segmented worm. Ragworms (what?)

a. only live on land.
b. have a backbone.
c. lack digestive systems.
d. have circulatory systems.