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,the head og a tape is constitued by a sucker and
Roundworms or Nematoda
Segmented Worms or Annelida
- Earthworms- Polychaetes- Leeches
Where do they live?
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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