Annelids - Worms with SegmentsOoooh. Worms. Walk around school after a rainstorm and you will have seen annelids. Earthworms are the classic example of annelids. Annelids are all of the segmented worms. Earthworms have little sections.
Body Parts in SectionsThey are special. The whole segmentation thing is the big one. They actually have loads of body parts that are duplicated in each segment. If one segment is damaged, some annelids can go on living. You are not segmented. You have one of everything. If you lose something... Too bad. They also have something called a closed circulatory system. It doesn't seem that amazing because you have one. However, as far as developed creatures, annelids were one of the first. They circulate nutrients and compounds through their segments using tubes. Other creatures with open systems just let everything move around on its own. Closed circulatory systems are more efficient.
More Efficient MovementLiving on land brings several problems. When you live in the ocean or fresh water like an octopus or jellyfish, moving isn't much of a problem. Specifically, gravity isn't such a big issue. When you're on land, you gotta move. You gotta get to food. You gotta hide from predators. You gotta find other worms to reproduce.
Annelids are able to move around by contracting their little segments. They have parts called setae. Setae are two pairs of hairs on each segment. Those hairs help some annelids (earthworms) get a grip on the soil. They are able to move through the soil easier with those setae. Those setae help other annelids called tubeworms grip the inside of their tubes so that they can move in and out more efficiently.
When you look at all of the creatures of the world, remember this... It's all about efficiency. That's what helps you, your species, and your world survive. If you are a parasite and you kill your host before you reproduce, you're out of luck. It's not efficient. You have an advantage when you are efficient. That advantage is what makes life easier for you. And, if you can pass that advantage on to your kids (better eyes for finding food), so much the better.
Invasion of the Earthworms (US-NSF Video)