Phyla Identification: Jointed Legs

The phylum of animals characterized by having jointed legs is Arthropoda.

Understanding Arthropods

Arthropods are defined by several key features, most notably their segmented bodies, a hard exoskeleton, and jointed appendages. These jointed appendages include their legs, antennae, and mouthparts, which are crucial for locomotion, sensing the environment, and feeding.

• Jointed Legs: This is the defining characteristic mentioned in the question.
• Exoskeleton: A protective outer covering made primarily of chitin.
• Segmentation: Bodies are typically divided into head, thorax, and abdomen.

Why Other Options Are Incorrect

The other phyla listed do not primarily feature jointed legs:

• Echinodermata: Includes organisms like starfish and sea urchins, known for radial symmetry and tube feet, not jointed legs.
• Annelida: This phylum includes segmented worms (e.g., earthworms) that have bristles (setae) but lack jointed legs.
• Nematoda: Commonly known as roundworms, these are unsegmented worms without jointed appendages.

Therefore, based on the defining characteristic of jointed legs, Arthropoda is the correct phylum.