Worms 2BIbDF09 10/11

What is a worm ?

Worms are invertebrate animals. They are multicellular with true tissues and bilateral symmetry and they have a soft and flexible body. [They are protostomes.] They probably appeared at the beginning of cambrian era and they are an important step of animals' evolution. There are several Phyla and each one live in a specific environment. Some of them are parasitic organisms that can live in a body or just live in soil or in the sea.

How are they classified ?

Worms are separate in three classes, depending on their body shape

- Flatworms or Platyhelminthes
That contain the :

• Tapeworms

- Roundworms or Nematoda
That contain the :

• Hookworms
• Pinworms

- Segmented Worms or Annelida

That contain the:

• Earthworms
• Polychates

• Leeches

What are the characteristics of each one?

flatworms or Platyhelminthes

General physical characteristics: Platyhelmintes are flat and they can measure about 1mm to 20m in length. They have no distinctive head or apppendix but they have a single opening that serve them to eat and to defecate.The are billaterians but they neither have body cavities, nor respiratory or circulatory organs.

The Phylum of Platyleminthes includes four sub-groups:

• the Turbellaria, they are mostly non-parasitic organisms, they live in water or in moist environnements. They can mesure from 1mm to 60cm and they are mostly all predators or scavengers and hermaphrodites.
• The Cestoda, or tapeworms are parasitic organisms. They mostly live in vertebrates intestines. Their head(scolex) is constitued by a sucker and a hook that allow them to attach to the intestinal wall. The tapeworm grow and feed itself absorbing and digesting the nutrients that the

Roundworms or Nematoda

====General physical characteristics :==== Roundworms or Nematoda are round, slender, and they measure typically less than 2.5 mm long; The smallest one is microscopic, but free-living species can reach as much as 5 mm and some parasitic species ca be larger. Their body have.

Segmented Worms or Annelida

- Earthworms- Polychaetes- Leeches

What are their part in the body features' evolution?

very disappointing... we started this wiki on Nov29... Be careful... you should now produce a big amount of work in order to have enough information on your page and for you oral presentationPierre.brawand 16 janvier 2011 à 16:02 (CET)

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