AY Honors/Worms/Answer Key

1. What is a worm?

A worm is an elongated soft-bodied invertebrate (boneless) animal. The best-known is the earthworm, but there are hundreds of thousands of different species that live in a wide variety of habitats other than soil.

2. Where do worms live?

Worms live in a variety of habitats, including in the soil, leaf litter, under rocks, in the water, and even inside the bodies of other animals.

3. What do worms eat?

Worms "eat" soil, which is to say that they swallow it, and as it passes through their bodies, nutrients are extracted from the organic materials found in the soil (such as dead leaves).

4. What kingdom are worms found in?

Worms are found in the Animal Kingdom.

5. Name the 3 major phyla (the next largest category of classification) that contain worms, and describe them.

Annelida (segmented worms)

The annelids are a large phylum of animals, comprising the segmented worms, with about 15,000 species including the well-known earthworms and leeches. They are found in most wet environments, and include many terrestrial, freshwater, and especially marine species, as well as some which are parasitic or mutualistic. They range in length from under a millimeter to over 3 meters (the seep tube worm Lamellibrachia luymesi).

Nematoda (roundworms)

The nematodes or roundworms are one of the most common phyla of animals, with over 20,000 different described species (over 15,000 are parasitic). They are found in great quantities in almost all freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts. They are found in locations as diverse as Antarctica and oceanic trenches. Further, there are a great many parasitic forms, causing disease in most plants and animals, humans included.

Platyhelminthes (flatworms)

The flatworms are a phylum of relatively simple soft-bodied invertebrate animals. With about 25,000 known species they are found in marine, freshwater, and even damp terrestrial environments. Most are free-living forms, but many are parasitic on other animals.

Other Worm Phyla

According to Wikipedia, worms belong to ten different phyla. The three most familiar are listed above, but for completeness, we mention the other seven here:

• Acanthocephala (spiny-headed worms)
• Chaetognatha (arrow worms)
• Gnathostomulida (jaw worms)
• Nematomorpha (horsehair worms)
• Nemertea (ribbonworms)
• Onychophora (velvet worms)
• Sipuncula (peanut worms)

6. What do “free living” and “parasitic” mean?

A parasitic creature (that is, a parasite) is one that lives off another, usually larger creature (a host) for a prolonged period of time. The parasite gains benefit from the relationship while the host is harmed. The "prolonged" portion of this definition distinguishes the predator/prey relationship from the parasite/host relationship. It also exludes brief relationships such as a mosquito bite. Examples of parasites include leeches, tapeworms, and nematodes.

A free-living creature is any creature that is not a parasite.

7. Which phyla, mentioned in question 5, are free living or parasitic?

Annelida include earthworms, which are free-living, and leeches, which are parasites. Most Nematodes (roundworms) are parasites, and most Platyhelminthes (flatworms) are not.

References:

• http://www.amonline.net.au/factsheets/earthworms.htm