The Phylum Annelida

The Phylum Annelida

The Phylum Annelida Amy Brown Science Stuff This phylum consists of segmented worms. These segmented worms may live in fresh water, salt water, or on land. This phylum is divided into three classes:

Phylum Annelida The term annelid means little rings. This name refers to the many body

segments that compose the body of a segmented worm. There are about 15,000 species of worms in this phylum. They all have: Bilatera l

Symmet ry A True Coelom Segmenta tion Three Germ Layers: Endoderm, Ectoderm and Mesoderm

Setae and Parapodia Setae: external bristles on the body; used for movement Parapodia: fleshy appendages on each side of most body segments The number of setae and the presence or absence of parapodia is the basis for dividing

the annelids into the three classes. Class Oligochaeta Generally live in the soil or fresh water. These worms have no parapodia. The word oligochaeta means few bristles. These worms have very few setae. This class includes the earthworms. External Structures

of the Earthworm 1) Prostomium / Mouth 2) Setae 3) Clitellum 4) Cuticle 5) Anus It is the first body segment in an earthworm. Prostomiu m

It is in front of (but does not include) the mouth. It is a lip-like extension over the dorsal surface of the mouth. Cli t

m ellu Contains both male and female reproductive structures. Setae In earthworms, there are 4 pairs of setae per segment. They

are used for movement. They anchor the worm in the ground as the longitudinal and circular muscles contract and expand. Cuticle The cuticle is a waxy, outer covering.

It prevents water loss and enables gases to diffuse through the skin. Movement of the Earthworm Circular and longitudinal muscles line the interior body

wall of the earthworm. The setae are used to anchor the worm in the ground. Circular muscles contract making the

earthworm longer. Longitudinal muscles contract making the earthworm shorter. Internal Structures of the Earthworm 1)

2) 3) 4) 5) 6) 7) Prostomium Pharynx Aortic Arches Esophagus Crop

Gizzard Seminal Receptacles 8) Seminal Vesicles 9) Sperm duct 10) Intestine 11) Clitellum 12) Setae Feeding and Digestion 1. Earthworms ingest soil as they burrow through it. 2. Soil is sucked into the mouth by a

muscular pharynx and then passes down the esophagus. 3. The soil and food enters the crop a temporary storage area. 4. From the crop soil moves into the gizzard. The gizzard is thick and muscular. The gizzard grinds the soil, releasing and breaking up organic matter.

5. As the soil passes through the intestine, digested organic compounds and nutrients from the soil are absorbed into the bloodstream. 6. Undigested material is eliminated from the body through the anus. Did you know that the earthworms digestive system is very helpful to us? a. Earthworms fertilize the soil by taking in decaying organic matter and eliminating the

wastes. b. The burrows made by earthworms allow air to penetrate into the soil, bringing oxygen to plant roots and other living organisms. c. Earthworms loosen the soil, making it easier for plant roots to grow, and for water to seep in. The earthworm has a closed circulatory system.

What is the purpose of the circulatory system? The purpose of the circulatory system is to transport oxygen, carbon dioxide, nutrients and wastes through the body of the worm. Respiration and Excretion How are oxygen and carbon dioxide

exchanged? Why must the skin stay moist? How does the skin stay moist? What are nephridia? O2 and CO2 diffuse directly through the skin. Just under the skin is a series of very small blood vessels. The gases diffuse through the skin and into and out of

bloodmoist vessels. mustthese remain for the The skin diffusion of gases to occur. Gases cannot diffuse across a dry surface. The skin is covered by a thin cuticle as well as mucus to keep it moist.

Nephridia are excretory tubules found just under the skin. They eliminate cellular wastes and excess water. Nervous The nervous system consists of several System ganglia and a ventral nerve cord. Ganglia: A mass of nervous tissue that serves as a very primitive brain.

The ganglia (anterior brain) can respond to simple stimuli such as light, touch, chemicals, moisture, temperature and vibrations. There are no specialized sense organs. Reproduction Hermaphrodi tic: A single

worm has both male and female reproductive organs. Sperm is produced in the testes and stored in the seminal vesicles. Mating occurs when two worms fuse their bodies together at the clitellum.

They exchange sperm; the exchanged sperm moves into the seminal receptacle where it is stored. The exchange of sperm occurs through the sperm duct. After several days, the clitellum secretes a tube made of mucus and a carbohydrate called chitin. Fertilization occurs in this tube. Class Polychaeta

The term polychaete means many bristles. This refers to the many setae that help polychaetes move. Polychaetes differ from other worms in that they have antennae and

specialized mouthparts. Class Hirudinea This is the smallest class of annelids. It consists of only 300 different species of Leeches are parasites. They have leeches. Leeches have no setae.

a sucker that is used to attach to the host body and suck blood. They secrete two substances: an anesthetic to prevent the host from feeling it, and another substance to prevent the blood from clotting. Leeches are often used for medicinal purposes. Leeches are used to suck out

blot clots from a wound, to promote circulation, and to relieve pressure in a joint or wound. What are the advantages to a segmented body? Body segmentation makes it possible for different parts of the body to contract or expand independently of the other segments.

Some organ systems can be duplicated in several different segments which provides How do polychaetes differ from earthworms? Polychaetes have more setae than earthworms. Most polychaetes live in marine environments. Most earthworms live in the soil. Polychaetes may have

antennae and advanced mouthparts. How are some leeches adapted to a parasitic way of life? Leeches have suckers to attach to the host to suck blood. Leeches secrete an anesthetic to prevent the host from feeling their presence. They secrete a second substance to prevent the

blood from clotting. How are the parasitic leeches different from the other parasitic worms such as the tapeworms and liver flukes? 1.Leeches are external parasites where the tapeworm and fluke are internal parasites. 2.The flukes must cycle between two hosts, a primary

Why do the earthworms require a moist environment? The earthworm exchanges gases (carbon dioxide and oxygen) by diffusion across the skin surface. This exchange can take place only if the skin is moist.

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