Biology-Mr. Willets
The Worms
There are 3 main phylums of animals called worms. The simplest of these is Phylum Platyhelminthes which are the flatworms. Most of these are aquatic, some live in moist soil and some are parasites.
The free-living (non-parasitic) flatworms are generally called planaria. These have bilateral symmetry with cephalization. The anterior end has eyespots and sensory lobes. The brain is located here also.
The main nerves resemble a ladder with two long nerves and many cross nerves.
Planaria are sedentary (slow moving) and are mostly scavengers. They have a GVC with one opening. This gut extends the full length of the body to help distribute digested food.
They have a flat body which makes it easier for oxygen to diffuse to all the cells. They have no circulatory system to do this. Flatworms are acoelomates - they have no body cavity.
Reproduction is almost completely sexual (some planaria can "rip" themselves in two). Planaria can be either separate sexed or hermaphrodites.
The parasitic flatworms are of two types- flukes and tapeworms.
Flukes live in various parts of your body and enter your body in your food or by boring through your skin. The fluke's eggs leave in your feces. While outside your body, they enter a snail (secondary host) and reproduce asexually to increase their numbers. The symptoms of fluke infection vary depending on where in your body they are living.
Tapeworms live in your intestines and use your digested food. As a result, you lose weight and have no energy in spite of eating normal amounts. The anterior end of the tapeworm called the scolex has hooks and/or suckers to hold on. The rest of the tapeworm (sections called proglottids) is essentially used for reproduction. Tapeworms produce millions of eggs which leave in your feces. They may end up in the grass where they are eaten by cows. The worms then go to the cow's muscles and form protective cysts. If you eat undercooked infected beef, the cysts go to your intestines, break open, attach and grow. Beef is inspected for tapeworm cysts before it is sold to you. If your doctor suspects you have a tapeworm, he will send a sample of your feces to a lab to look for tapeworm egg cases (proglottids). The treatment involves irritating the tapeworm so that it lets go and the entire worm leaves in the feces. This treatment gives you a bad case of diarrhea.
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Phylum Nematoda contains the round worms. These are terrestrial (on land), aquatic and parasites.
They have a complete gut with a mouth and anus. Their body has a cavity where the internal organs are located but the internal organs are not attached to the body wall. This means they are pseudocoelomates.
There are several common parasitic roundworms (these are not common in the USA):
Ascaris- very common in animals and humans. These live mostly in the intestines but can be found in other parts of the body. Their eggs enter the body in our food and leave with our feces. They are easily removed from the intestines since they have no method of holding on. If your dog has worms, it is probably this kind.
Hookworm-these live in the intestines but feed on blood that flows from where their jaws attach. The symptoms of this worm are as a result of blood loss: lack of energy being the most obvious. The blood loss is much more harmful to younger children because it slows their mental development. The eggs of these worms leave in the feces and the larva live in the soil. These larva can bore into our feet, travel through the blood to our lungs, crawl up to our throat where we swallow them. They then hook on inside our intestines.
Trichina worm-The adult lives in our intestines where it reproduces. The offspring travel through the blood and form painful cysts in our muscles. We get this by eating infected pork. The infected pig got the worms by eating some other infected animal. This is a disease of meat eaters. We do not pass it on unless some animal eats us.
Filarial worms- These worms are carried from animal to animal by insect vectors. A common example is heartworm in dogs. In humans, a disease called elephantiasis is caused by this type of roundworm. These worms block the flow of lymph and cause enormous swelling of the legs (hence the name-elephantiasis).
Questions-
1) The free-living flatworms are called _____________________________ What sense organs are found at the anterior end of these worms? _____________________________________________
Having sense organs at the anterior end is called _______________________________
2) Why is the flatworm nervous system called a "ladder type" nervous system? _____________________
_____________________________________________________________________________
3) The gut of planaria is a GVC. What do these letters stand for? ________________________________
It is called this because besides digesting the food, it also _______________________________ it. To do this, the gut extends the ____________________________ of the body.
4) Planaria are sedentary. What does this mean? __________________________________________
5) Flatworms are flat (duh!) Why? ___________________________________________________
They must be flat because they have no ____________________________ to help move materials around.
6) Flatworms have no body cavity for the internal organs. They are _____________________________
7) The two types of flatworm parasites are __________________ and _____________________
8) Which flatworm parasite spends some time in a snail? __________________
9) Which flatworm parasite has hooks and suckers? ________________________ These are located on the anterior end called the ____________________
10) The sections of the tapeworm that are mostly reproductive are called _______________________
11) We can get tapeworms by eating infected ___________________ This animal got the worms by eating
__________________ that contained the eggs.
12) Most flatworm parasites enter our bodies with our ________ and their eggs leave with our _________
13) Roundworms are in what phylum? _______________________
14) The gut of roundworms has 2 ______________. They are the ____________ and ___________
This is called a ________________________ gut.
15) Roundworms are pseudocoelomates. They have a body _____________________ but the internal organs are not ____________________ to the inner body wall.
16) Even though it lives in our intestines, the hookworm feeds on ___________________ The hookworm's eggs leave in our ______________ and the larva live in the _______________ They enter another person by _____________________________________. Once inside the blood, they eventually go to the _________ and then up to the _______________ where they are swallowed.
17) Trichina worm can form ___________________ in our muscles. We get this worm by eating infected ____________. We can only get this worm by eating animals that eat _____________.
18) How do filarial worms get from person to person? ___________________________ What disease of dogs is caused by these worms? _______________________ What disease in humans? __________________________________