What are the characteristics of the groups Annelida, Mollusca, Arthropoda, and Echinodermata?

Annelida have a soft, elongated, and cylindrical body, divided into rings. Earthworms belong to this group.
Mollusca have a soft body, sometimes protected by a shell. Examples of Mollusca are octopuses and snails.
Arthropoda have a segmented body protected by a shell. Examples of Arthropoda are spiders, shrimps, and butterflies.
Echinodermata are animals without a head and with the body covered in spines and plates. Starfish belong to this group.