Invertebrates Flat, Round, & Segmented Worms

III. Phylum Platyhelminth (Flat Worms) The phylum Platyhelminthes represents all flatworms in the kingdom Animalia. Flatworms are hermaphroditic (they have both male and female sex organs) and are capable of sexual and asexual reproduction.

Marine Flatworms GxA

Marine flatworms are arguably among the most beautiful creatures in the sea.

Parasitic Flatworms are responsible for a number of animal diseases…

Tapeworms are parasitic flatworms that infect the digestive tracts of animals. They hook into the intestine and absorb the digested nutrients. They can grow very long and spread quickly. Several species can infect human hosts. Imagine having a 10 to 30 foot long tapeworm in your intestines…. The longest tapeworm ever removed from a human came out of Sally Mae Wallace on September 05, Doctors pulled a 37 foot long tapeworm out through her mouth.

Doctor removes a tapeworm from a human host.

Fish are common carriers of certain types of tapeworm.

Parasitic flatworms called schistosomes or “blood flukes” cause the disease Schistosomiasis. The blood fluke is carried by certain species of freshwater snails who infect water sources with their waste. Though seldom fatal, the disease can cause serious debilitation and damage to the liver and intestines.

IV. Phylum Nematoda (Round Worms) Roundworms are small, cylindrical, un-segmented worms that pervade the soil, bodies of most other animals, and aquatic ecosystems. They are very successful and can live almost anywhere, such as in soil, as parasites in higher animals, plants, and in water. Most of them are so small that they are not even noticed. Nematodes are almost unbelievably abundant. One study reported around 90,000 individual nematodes in a single rotting apple. Another reported 236 species living in a few cubic centimeters of mud. The number of described species is around 12,000, but too little attention has been paid to these animals and the true number may be closer to 500,000. Many nematodes are free living and play critical ecological roles as decomposers and predators of certain harmful insect larvae and microorganisms.

But nematodes also include parasitic species, a number of which affect humans directly or indirectly through their domestic animals. These include the common roundworms, which may infest more than half the world's humans; hookworms; trichina, the worms that cause trichinosis; pinworms, another extremely common parasite, even in the United States, which can be transmitted from human to human by eggs floating in household dust; and filarial worms, primarily tropical parasites that cause diseases such as filariasis (elephantiasis) and onchocerciasis (river blindness).

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Hookworms

The trichina worm is a parasite that lives in muscles of man and animals. Trichinosis is caused by eating undercooked pork, especially from wild boars.

Pinworm is the most common worm infection in the United States. School-age children, followed by preschoolers, have the highest rates of infection. In some groups nearly 50% of children are infected. Infection often occurs in more than one family member. Pinworms are about the length of a staple and live in the rectum of humans.

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Filariasis (aka “elephantitis) is caused by a roundworm that blocks the lymph nodes in the body and causes them to swell.

Guinea worms grown enter humans through the intestinal track, but migrate and grow under the skin. Guinea worm infections are very common in parts of Africa.

River Blindness, or Onchocerciasis, is the world's second leading cause of blindness. Although rarely a life threatening disease, Onchocerciasis causes chronic suffering and severe disability among 18 million people worldwide, of whom 300,000 are irreversibly blind. The disease is mostly encountered in the Western and Central Africa, and to a lesser extent in the Middle East and the Americas.

Make sure you give your pets their heartworm medicine every month.

V. Phylum Annelida (Segmented Worms) Annelids make up a large phylum of animals comprising the segmented worms, with about 15,000 modern species including the well-known earthworms and leeches. They are found in most wet environments, and include many terrestrial, freshwater, and especially marine species (there are over 8,000 species of marine annelids!) Annelids are distinguished by ring-like external bands along their muscular body wall that coincide with internal partitions dividing their bodies into segments. Segmented worms have a closed circulatory system (as do we), a nervous system, and a true digestive system with a separate mouth and anus (thank goodness…). Most “breath” by absorbing oxygen through their skin. Some species of annelids are passive filter feeders (marine tube worms); some are decomposers (earthworms); some are parasites (leeches); and some are predators (many species of marine worm such as the clam worm). Some species are hermaphroditic (have both male and female sex organs.)

Some annelids have long appendages (known as parapodia) covered with bristles extending from each of their body segments.

Earthworms and leeches don’t have parapodia, but if you feel along the bottom of an earthworm, you can feel that the earthworm also has little bristles protruding from each segment. These setae help the earthworm to get a grip!

The vampire of the annelid world. Leeches….

Leeches are used in certain medical procedures to improve blood circulation to certain areas of the body. If you think that’s gross, wait ‘til we learn about medical maggots….

Polychaete marine worms (ones with parapodia).