what are the differences between annelida, mollusca and arthropoda ?

An arthropod is an invertebrate that has an exoskeleton, a segmented body, and jointed attachments called appendages, and an annelids have worm-like features. Molluscs have a soft, unsegmented body with bilateral symmetry. The basic molluscan body plan includes an internal or external shell lined with a sheet of tissue called the mantle. 

Following are the difference between annelida, arthropoda and mollusca-

Annelida:

1. Long, cylindrical and soft body divided into rings.

2. Exoskeletons are absent.

3. They have no jointed appendages.

4. Excretion occurs through nephridia.

5. Respiration occurs through skin or parapodia. 

Athropoda:

1. Body is divided into head, thorax and abdomen.

2. Body is covered by chitinous exoskeletons.

3. They have jointed appendages.

4. Excretion occurs through coxal gland on malpighian tubules.

5. Respiration occurs through tracheae, gills or book lungs. 

Mollusca:

1. Soft body divided into three distinct parts- a distinct head, visceral mass and muscular foot.

2. Body is covered by calcareous shell.

3. They have distinct foot for moving around.

4. Excretions occurs through nephridia.

5. Respiration occurs through gills.