Does an earthworm have a brain?
Just like you, earthworms do have a brain. Their brains are much simpler than yours, however. Earthworms’ brains allow them to sense and respond to light and touch.
Segmented worms are in the phylum Annelida , which has over 22,000 known species. These worms are known as the segmented worms because their bodies are segmented, or separated into repeating units. Besides the earthworm, the segmented worms also include leeches and some marine worms. Most segmented worms feed on dead organic matter, like the earthworm. Leeches ( Figure below ), however, can live in freshwater and suck blood from their animal host. You may have noticed many earthworms in soil. Earthworms support terrestrial ecosystems both as prey and by aerating and enriching soil.
Leeches are parasitic worms. Notice the presence of segments.
Features of Segmented Worms
Segmented worms have a number of characteristic features.
- The basic form consists of multiple segments, each of which has the same sets of organs and, in most a pair of parapodia that many species use for locomotion.
- Segmented worms have a well-developed body cavity filled with fluid. This fluid-filled cavity serves as a hydroskeleton , a supportive structure that helps move the worm's muscles.
- Segmented worms also tend to have organ systems that are more developed than the roundworms' or flatworms'. Earthworms, for example, have a complete digestive tract with two openings, as well as an esophagus and intestines. The circulatory system consists of paired hearts and blood vessels. Actually there are five pairs of hearts that pump blood along the two main vessels. And the nervous system consists of the brain and a ventral nerve cord.
Comparison of Worms
The following table compares the three worm phyla ( Table below ).
|Type of Worm||Body Cavity||Segmented||Digestive System||Example|
- hydroskeleton : Fluid-filled cavity used as support for contracting muscles.
- leech : Segmented worm that feeds on the blood of animals.
- parapodia : Paired, un-jointed lateral outgrowths used for locomotion.
- segmented worm : Worm with a body plan of repeating segments.
- Segmented worms include the common earthworm and leeches.
- Segmented worms have a digestive system, nervous system, and circulatory system.
Use the resources below to answer the questions that follow.
- Annelids: Powerful and Capable Worms at http://vimeo.com/37255842 (13:38)
- What new realms did animals like Abarenicola open up for other animals?
- Where are the eyes of feather duster worms ( Sabellidae ) located?
- What effect do tube dwelling worms have on mudflat ecosystems?
- How much can a giant tube dwelling worm from a hydrothermal vent grow in a year? Given that some of these vent communities last less than a decade, how is this growth advantageous to the animal?
- How do earthworms help breakdown leaf litter? Be as specific as you can in your answer.
- The Leech - Discovery Kids at http://kids.discovery.com/home/the-leech
- What are some ways a doctor might use a leech?
- Do leeches eat often?
- What features distinguish Phylum Annelida from the other worms?
- Describe the skeletal system of the segmented worms.