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 no body cavities - Tapeworms

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