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Earthworms, Christmas Tree Worms, Leeches, and Other Annelids
Annelids are segmented worms, like earthworms and leeches.
Annelids (animals belonging to the Annelid Phylum which is in the Animalia Kingdom) are segmented worms including earthworms, leeches, fireworms, Christmas Tree worms, and many other species. Having segments is one of the primary characteristics that separates annelid worms from flatworms and roundworms. These segments are rings that repeat all up and down the worm's body.
Most annelids live in the ocean, but others, like the earthworm, live on land. You may be surprised when you see some of the photos of the marine annelids below - as they just don't look like worms at all! Have you ever seen a Feather Duster worm?!
Characteristics of Annelids - Segments, coelom, bristles, closed circulatory system, and more
- Segmentation - Each segment in a segmented worm contains many of the same organs, including those used in digestion, movement, excretion (getting rid of waste), and circulation. In the photo above, you can easily see the individual segments of the worm.
- Septa - Septa are internal walls that separate the body segments. They can be found in most types of annelids. The worm's circulatory system allows nutrients and other things to be passed from one segment to another.
- Cerebral ganglion - A cerebral ganglion is a primitive brain that is located in a segment near the front of the worm.
- A nerve cord connected to the brain runs along the underside of an annelid's body. This nerve cord carries sensory information from the various segments to the worm's brain.
- Coelom - A coelom is a fluid filled cavity located between the gut and the body wall. The coelom of an annelid is a true coelom because it's located entirely within the mesoderm (muscle tissue). For more about the coelom, please visit: The Types of Bodies Animals Have.
- Closed circulatory system - Like humans, annelids have a closed circulatory system. That means that the blood pumped by the heart is fully contained within the circulatory system and does not wash out into the tissues of the body.
- Annelids have highly specialized organs.
- Nephridia are excretory organs which remove wastes from the annelid's body.
- Setae are bristles that are located on each segment of some annelids. Setae help increase traction to make movement easier for the worm.
- Parapodiaare almost like a series of little feet. Parapodia are paired and unjointed appendages (things that stick out from the main part of the body are called appendages.). Some, but not all, annelids have parapodia.
Did you know that annelids can be anywhere from 1 mm (.04 inches) long to over 3 meters (10 feet) long?! A 3 meter long worm?! Wow!Check out the video below on "Giant Earthworms!"
There's a lot of variety to the worms that make up the Annelid phylum!
What? These are all worms??
Yes. These are segmented worms in the annelid phylum.
Feather Duster Worm
Christmas Tree Worm
More Christmas Tree Worms
Good Worms, Bad Worms
Leeches are a "blood sucking" type of annelid
Leeches are different from many annelids in that they do not have bristles (setae). Also, the external segmentation of their bodies does not match up with the internal segmentation of their organs. Because there is not much empty space in their coeloms, the bodies of leaches are much more solid than those of most annelids.
Leeches can live in water (fresh water or marine) or on land.
Another characteristic of leeches is that they have two suckers, one one each end of their bodies. Leaches use these suckers to get blood from other animals.
Leeches are sometimes used for medical purposes. The video below explains more about how leaches are used to help people get well.
Did you know?
Did you know that leeches have a substance in their salvia called hirudin which helps prevent the blood of their "victim" from clotting?
Earthworms are a type of annelid - The characteristics of earthworms
- No parapodia (Parapodia are the feet-like appendages on the sides of some annelids.)
- Only a few setae per body segment. (Setae = bristles.)
- Earthworms do not have eyes, but they can sense light. Earthworms do not like light and will move away from it when possible.
- Earthworms can eat their weight in soil every day!
- The soil earthworms eat goes from the mouth into the esophagus (throat) and then into the worm's crop. A crop is a "storage room." Next the soil moves into the gizzard of the worm. After the soil is broken down by a grinding action in the gizzard, it moves into the intestine. Here, some of the digested food is absorbed into the intestinal wall, while the rest moves on out of the body via the anus, forming castings.
- The skin of earthworms must remain moist, or the earthworms will die. This is because oxygen and carbon dioxide can only pass through an earthworm's skin if the skin is moist.
- Earthworms are hermaphrodites which means that each earthworm contains both male and female reproductive organs. To mate, earthworms join at their clitella (located about a third of a way down mature earthworms) and exchange sperm. Both worms then form an egg capsule which is shed after about 7 to 10 days in their castings. 14 to 21 days later, baby worms hatch. Each egg may contain between 1 to 5 baby earthworms! It takes between 60 and 90 days for the baby earthworms to become adults.
Observing Live Worms Is An Excellent Way To Learn More About Them! - Worm Composting
Worm Composting invovles preparing some sort of box (with air holes that are small enough the worms can't escape) for the worms to live in. You feed the worms scraps of vegetable peels, etc, and as they eat the food scrapes, they turn the scraps into wonderful compost you can use in your garden! Worm composting is a great way to learn more about worms!
The kids in our homeschool co-op did worm composting as a project one year. They uses plastic tubs with lids. One of the parents drilled tiny holes in the tubs, so the worms could breath. For more info, please refer to one of the books below, or visit: Worm Composting Basics.
Let's see what you've learned about earthworms!
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An Earthworm's Life
A list of webpages in this biology series
Homepage: Biology: Information, Videos, and Labs
Unit 1 on Cell Biology
Unit 2 on Genetics
Unit 3 on The History of Life on Earth
Unit 4 on Ecology
Unit 5 on Diversity
Unit 6 on All About Plants
Unit 7 on The Animal Kingdom: Invertebrates
Unit 8 on Vertebrates
Check back later for additional biology units!
Were you surprised that some of these species are called worms? Which one is your favorite?
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