Segmented Worms

Ch. 13, pgs. 369-373

Segmented Worm Characteristics

� Segmented worms are in the phylum annelida.

� Annelids have tube shaped bodies that are divided into many segments.

� On the outside of each body segment are bristle-like setae.

� Segmented worms use their setae to hold on to the soil and move.

Segmented Worm Characteristics

� Segmented worms have bilateral symmetry.

� Segmented worms have a body cavitythat holds the organs.

� Segmented worms have two openings—amouth and an anus.

Segmented Worm Characteristics

� Annelids can be found in freshwater, salt water, and moist soil.

� Examples are:

Marine Worms Earthworms Leeches

Earthworms

Earthworm Body Systems

� Earthworms have a definite anterior and posterior.

� Anterior – front end.

� Posterior – back end.

� Earthworms have more than 100 body segments.

� Each body segment, except the first and last segments, has 4 pairs of setae.

Earthworm Body Systems

� Earthworms move by using their setae and two sets of muscles in the body wall.

� One set of muscles runs the length of the body.

� The other set of muscles circles the body.

Earthworm Body Systems

� When an earthworm contracts its long muscles, it causes some of the segments to bunch up and the setae to stick out.

� This anchors the worm to the soil.

� When an earthworm contracts its circular muscles, the setae are pulled in.

� This allows the worm to move forward.

Digestion and Excretion

1. Earthworms take in soil and get energy from the bits of leaves and other organic matter found in the soil.

2. The soil ingested by an earthworm moves to the crop.

� The crop is a sac used for storage.

Digestion and Excretion

3. Behind the crop is a muscular structure called the gizzard.

� The gizzard grinds the soil and the bits of organic matter.

4. The ground material passes through the intestines, where organic matter is broken down and absorbed by the blood.

5. Wastes leave the body through the anus.

Circulation

� Earthworms have a closed circulatory system.

� A closed circulatory system is a blood circulation system in which blood moves through the body in closed vessels.

Circulation

� Earthworms have two blood vessels along the top of the body and one blood vessel along the bottom of the body.

� These blood vessels meet at the front of the body and connect to heart-like structures called aortic arches.

Respiration

� Earthworms do not have gills or lungs.

� Oxygen and carbon dioxide are exchanged through the skin, which is covered with a watery mucus.

Nerve Response

� Earthworms have a small brain in their front body segment.

� Nerves in each segment join to form a nerve cord that connects to the ganglion, or “brain”.

Reproduction

� Earthworms are hermaphrodites.

� Hermaphrodites produce both sperm and egg in the same body.

� An earthworm cannot fertilize its own eggs!

� It must receive sperm from another earthworm to reproduce.

Reproduction

� Once the eggs are fertilized, the earthworm forms a clitellum.

� The clitellum is a “band” that produces and secretes mucus to make a protective cocoon for the eggs.

Value of Earthworms

� Earthworms help aerate the soil by burrowing through it.

� By eating soil, earthworms speed up the return of nitrogen and other nutrients to the soil.

Marine Worms

Fan worms

Fan worms

Free-swimming worm

Marine Worms

� Marine worms are called polychaetes.

� Like earthworms, polychaetes have segments with setae.

� However, setae occur in bundles in these worms.

� The word polychaete means “many bristles”.

Marine Worms

� Marine worms float, burrow, build structures, or walk along the ocean floor.

� Sessile, bottom dwelling polychaetes have specialized tentacles for exchanging gases and gathering food.

Marine Worms

� Some marine worms build tubes around their bodies.

� When startled, these worms retreat into their tubes.

Marine Worms

� Free-swimming polychaetes, such as the bristle worm, have a head with eyes, a tail and parapodia.

� Parapodia are paired fleshy outgrowths located on a bristle worm’s segments.

� Parapodia help with feeding and locomotion.

Leeches

Leeches

� Leeches are segmented worms, but their bodies aren’t as round and they do nothave setae.

Leeches

� Leeches feed on the blood of other animals.

� Leeches produce many chemicals, including an anesthetic, that numbs the wound so you won’t feel the bite.

� Leeches prefer blood, but can also survive by eating aquatic insects and other organisms instead.

Leeches and Medicine

� Leeches are sometimes used after surgery to keep blood flowing to a repaired area.

� Leeches contain chemicals in their saliva that help dilate blood vessels and keep the blood from clotting.

Value of Segmented Worms

� Researchers are developing drugs from the chemicals in a leech’s saliva.

� Marine worms a good source of food for many fish, invertebrates, and mammals.