Ch. 1 Sec. 4

worm characteristicsinvertebrates

bilateral symmetry

simplest organism with a brain

sexual or asexual reproduction

regeneration= ability to regrow body parts

Biologists classify worms into three major phyla—flatworms,

roundworms, and segmented worms.

sheep liver flukepinworm

earthworm

3 majorgroups

of worms

1. flatworms

2. roundworms

3. segmented

worms

1. flatworms• most parasitesparasites= - live inside or on

another organism (host)

- can be harmful - eg. tapeworms• some free-living=free-living= - do not live in or on

other organisms - eg. planarians

Life Cycle of a Dog Tapeworm

tapeworm segment breaks releases eggs eggs are eaten by grazing flea larva

flea larva pupates

Rover licks himself and swallows fleas

As Rover sleeps, tapeworm segments are passed.

planariaplanaria

• scavenger= feeds on dead or decaying material• 2 eyespots• feeds like a vacuum cleaner - 1 opening in its digestive system (food enters mouth wastes exit mouth)

2 eyespots

2. Roundworms• live in moist environments• many - parasites • most abundant animal on

Earth

2. Roundworms

• 1 way digestive system- 2 openings

(food enters mouth wastes exit anus)

3. segmented worms

• bodies made of many segmentssegments= linked sections

• 1 way digestive system w/ 2 openings

• closed circulatory system

• examples:

1. leeches

2. earthworms

Earthworms and other segmented worms have bodies made up of many

linked sections called segments.

Segmented worms

earthworms

• obtain oxygen thru. moisture on skin

• wastes exit from anus

• droppings make soil fertile

Click here for virtual earthworm tour

What am I ?

flatworm

roundworm

segmented wormEddie & Eddie & LarryLarry

Paulette & Paulette & TommiTommi

Worm Interviews

Paulette the Planarian:

1. How does the planaria take in food?

2. What is regeneration?

3. Where can you find Planaria?

Click here for interview with Paulette Planarian

Tommi the Tapeworm:

1. What is a parasite?

2. What is a host?

3. Where do you find a beef tapeworm?

4. How big can they get?

Click here for interview with Tommi the Tapeworm

Larry the Leech: 1. What do leeches feed on?

2. How do they attach to their host?

3. Why are they used for medicinal purposes?

4. Why doesn't the blood clot?

5. How are leeches related to earthworms?

Click here for interview with Larry the Leech

Eddie the Earthworm:

1. What is mucous?

2. What do worms do for the soil?

3. How is a Night Crawler different than an earthworm?

Click here for interview with Eddie the Earthworm

Earthworm dissection

1. clitellum- organ responsible for mucus production during reproduction.

2. dark line - dorsal blood vessel

• 3. crop region of the digestive system

• 4. The arrow points to one of the worm's five pairs of “hearts” or aortic arches, located in segments 7-11

PART 2• 1) Place your earthworm in the dissecting tray with

the dorsal surface up and the anterior end facing away from you. Place dissecting needles through the first and last segments to hold the worm in position. In making an incision you must be careful to cut only the body wall. If you cut too deeply, you will damage the internal organs. The incision should be slightly to one side of the midline. Using a sharp scalpel or dissecting scissors, make an incision from behind the clitellum to the anus.

CAUTION:CAUTION: Handle the scalpel and scissors Handle the scalpel and scissors with caution throughout this lab activity.with caution throughout this lab activity.

• Then turn the tray around and extend the incision to the mouth. Holding the body wall with your forceps, use a scalpel to cut the membranes that separate the segments of the earthworm. Starting at the anterior end, separate the body wall along the cut, and pin it down.

• 2. Beginning at the anterior end of the worm (segment one), identify the organs of the digestive system. Use a probe to feel the relative thicknesses of the walls of the crop and gizzard. Use your scalpel to make a cross-sectional cut through the intestine about half way along its length. Make sure you cut only through the intestine; do not cut any other body part. Examine the cut end of the intestine with a hand lens.

• The earthworm has a closed circulatory system. Blood is pumped through vessels by five pairs of aortic arches, or hearts. The aortic arches encircle the esophagus between segments seven and eleven.

• 3) Identify the dorsal vessel, which runs along the top of the intestine. Follow it forward toward the esophagus. Gently move aside any organs that obscure your view so that you can see the aortic arches around the esophagus. Lift the cut end of the intestine so that you can see the ventral vessel, which runs along the ventral surface of the digestive tract.

• Earthworms are hermaphroditic-they contain both male and female reproductive structures. However, self-fertilization does not occur. When earthworms mate, they exchange sperm, which later will fertilize the eggs produced by the ovaries. Sperm are produced and stored in the seminal vesicles. Sperm received from another worm in mating are stored in the two pairs of seminal receptacles.

Observation: External Anatomy• Find the anterior (front) end of the earthworm by locating the

fleshy bump over its mouth, called the prostomium. The posterior (back) end has a small hole where solid waste is expelled, called the anus. The length of the worm is made up of many tiny segments, each separated by a thin wall called a septum.

• 2. About one-third of the way back from the mouth you should see a thicker and smoother section of the worm. This is called the clitellum, and it is involved in reproduction.

• 3. Notice that the earthworm has a rounded dorsal (back) surface and a flatter ventral (belly) surface. Usually the dorsal surface is darker than the ventral surface (though sometimes this is obscured in the preservation process). Lightly rub your finger along the ventral side toward the posterior end of the worm. You should feel a roughness caused by tiny bristles called setae. Using a magnifying glass, try to see the setae.

• 4. With your magnifying glass look for tiny pores on each segment. Liquid wastes are expelled through these pores. Near the front end of the worm you should see some larger pores that can be easily seen without magnification. These are genital pores and are important in reproduction.

• Pharynx: This is the light-colored organ just inside the mouth. Its muscular contractions pass food on down to the esophagus.

• Hearts (or "aortic arches"): Behind the pharynx are five dark loops wrapped around the esophagus. These are the blood vessels that serve as the hearts of the worm.

• Dorsal blood vessel: This is a dark line extending from the hearts over the top of the crop.

• Crop: Food from the esophagus is temporarily stored in the crop. • Gizzard: Food comes from the crop into the gizzard, where it is ground up. • Intestine: The intestine is the long tube extending from the gizzard all the

way to the anus. Food is digested and absorbed here. • Reproductive organs: The light colored tissue above and around the

hearts are seminal vesicles. Other reproductive parts appear as small white organs on the ventral side of the hearts.

• Ventral Nerve Cord: With your forceps, gently push aside the intestine to view the long white nerve cord running along the length of the worm beneath it.

YOU DID IT ! YOU’VE COMPLETED YOUR FIRST

DISSECTION !• NOW IT’S TIME TO CLEAN UP !

1. PLACE ALL OF THE DISSECTING EQUIPMENT ON THE DISSECTING TRAY.

2. PUT YOUR WORM, WITH ALL OF ITS PARTS, ALONG WITH YOUR GLOVES IN THE TRASH.

3. WHEN YOUR TABLE IS CALLED, WASH YOUR HANDS WITH SOAP AND WATER.