SEGMENTED WORMS
IN GENERAL

descending worms with glowing eyes... In our backyards the main segmented worms, or annelids, are earthworms. If you've ever looked closely at earthworms, you've probably decided that they're pretty simple affairs, maybe even less sophisticated than snails and slugs. However, that's not necessarily the case. Their anatomy indicates that, in evolutionary terms, annelids are more advanced than mollusks. Here are some of the ways annelids are more complex -- more "highly evolved" -- than mollusks such as slugs and snails:

HOW ANNELIDS ARE
MORE COMPLEX THAN MOLLUSKS

Despite these "improvements" over mollusks, annelids are by no means very sophisticated. They don't have anything as fancy as a skeleton, or an ability to keep their bodies warm when the temperature drops. Also, the problem with their bodies drying out remains critical, despite the cuticle. They don't have very big brains, either.

Here's something very interesting about segmented worms: If an explorer- naturalist from another galaxy came to Earth with the assignment of collecting an "average Earth-animal," after studying everything from the lowliest sponges, jellyfish, and flatworms, to us humans, there would be a fair chance that he/she/it would choose to take back an annelid. In other words, segmented worms stand about midway between the simplest and most complex of Earth's animals.

For an introduction to the annelids, you may be interested in reviewing at Amazon.com the book Earthworms, Leeches, and Sea Worms: Annelids.