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.

What are the three main classes of worms ?

There are separate in three classes that depending on their body shape, there are three main classes of worms :

- flatworms or Platyhelminthes :

- Tapeworms

- roundworms or Nematoda

- Segmented Worms or Annelida :

- Earthworms
- Polychaetes
- Leeches

What are the characteristics of each one?

flatworms or Platyhelminthes

Physical characteristic:

They are flat and they can measure about 1mm to 20m in length. They have a single opening that serve them to eat and to defecate. They have suckers that can attach to the inside of the blood vessels or in the human intestines. They have no body cavities

- Tapeworms

- roundworms or Nematoda - Segmented Worms or Annelida : - Earthworms- Polychaetes- Leeches