The question asks to identify the phylum of animals that possess jointed legs.

Phylum Identification Based on Jointed Legs

The defining characteristic mentioned is the presence of jointed legs or appendages. Let's examine the options:

• Nematoda: Commonly known as roundworms, they have smooth, unsegmented bodies and lack jointed legs.
• Arthropoda: This phylum includes insects, spiders, crustaceans, and centipedes. A key feature of arthropods is their exoskeleton and segmented bodies with jointed appendages, including legs.
• Echinodermata: This group includes starfish and sea urchins. They are characterized by radial symmetry and tube feet, not jointed legs.
• Annelida: These are segmented worms like earthworms. They have segmented bodies but lack jointed legs.

Therefore, the phylum characterized by animals with jointed legs is Arthropoda.