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 free-living.

8. Answer the following questions about earthworms.

a. Where do they live?

Earthworms live all over the world except in polar and arid regions.

b. What do they eat?

Earthworms feed on organic matter found in the soil, such as leaf litter. They pass soil through the gut, extracting nutrients from it as it passes through their bodies.

c. How are they helpful to humans?

The major benefits of earthworm activities to soil fertility can be summarized as:

Biological

The earthworm is essential to composting; the process of converting dead organic matter into rich humus, a medium vital to the growth of healthy plants, and thus ensuring the continuance of the cycle of fertility. This is achieved by the worm's actions of pulling down below any organic matter deposited on the soil surface (eg, leaf fall, manure, etc) either for food or when it needs to plug its burrow. Once in the burrow, the worm will shred the leaf and partially digest it, then mingle it with the earth by saturating it with intestinal secretions. Worm casts (see below) can contain 40% more humus than the top 6" of soil in which the worm is living.

Chemical

As well as dead organic matter, the earthworm also ingests any other soil particles that are small enough—including stones up to 1/20 of an inch (1.25mm) across—into its 'crop' wherein minute fragments of grit grind everything into a fine paste which is then digested in the stomach. When the worm excretes this in the form of casts which are deposited on the surface or deeper in the soil, a perfectly balanced selection of minerals and plant nutrients is made available in an accessible form. Investigations in the US show that fresh earthworm casts are 5 times richer in available nitrogen, 7 times richer in available phosphates and 11 times richer in available potash than the surrounding upper 6 inches (150 mm) of soil. In conditions where there is plenty of available humus, the weight of casts produced may be greater than 4.5 kg (10 lb) per worm per year, in itself an indicator of why it pays the gardener or farmer to keep worm populations high.

Physical

By its burrowing actions, the earthworm is of great value in keeping the soil structure open, creating a multitude of channels which allow the processes of both aeration and drainage to occur. Permaculture co-founder Bill Mollison points out that by sliding in their tunnels, earthworms "act as an innumerable army of pistons pumping air in and out of the soils on a 24 hour cycle (more rapidly at night)" (Permaculture- A Designer's Manual, Tagari Press, 1988). Thus the earthworm not only creates passages for air and water to traverse, but is itself a vital component in the living biosystem that is healthy soil.

d. How short and how long do they get?

Earthworms range in size from two centimeters (less than one inch) to over three meters (almost ten feet) in the Giant Gippsland Earthworm.

e. How many are there in one square meter of soil?

Recent research has produced figures suggesting that even poor soil may support 62 worms per square meter, while rich fertile farmland may have up to 432 worms pers square meter. In optimum conditions, the worm population may even reach 62,000 worms per square meter, meaning that the weight of earthworms beneath the farmer's soil could be greater than that of his livestock upon its surface.

f. How many species are there?

There are over 5,500 named species of earthworms worldwide.

g. What is the clitelum?

The Clitellum is a thickened glandular section of the body wall that secretes a cocoon in which the eggs are deposited. Once the eggs have been deposited in the cocoon, the clitellum slides off of the earthworm's body.

References:

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