Which phylum includes earthworms and leeches?

Which phylum includes earthworms and leeches?

• A. Annelida
• B. Arthropoda
• C. Mollusca
• D. Chordata

Answer: (A)

The main idea here is identifying which phylum groups earthworms and leeches. Both are segmented worms, built from repeated body units, and they possess a true coelom. They share a basic annelid body plan, including a closed circulatory system and a body divided into rings (segments) that function together. This combination of segmentation and coelom is the giveaway that they belong to Annelida, not to other major invertebrate groups. For context, the other options describe groups with different defining traits. Arthropods have an external skeleton (exoskeleton) and jointed limbs; Mollusca typically have a muscular foot, a mantle, and often a shell; Chordata possess a notochord and dorsal nerve cord at some stage. Earthworms and leeches lack these features, which is why they sit in Annelida.

The main idea here is identifying which phylum groups earthworms and leeches. Both are segmented worms, built from repeated body units, and they possess a true coelom. They share a basic annelid body plan, including a closed circulatory system and a body divided into rings (segments) that function together. This combination of segmentation and coelom is the giveaway that they belong to Annelida, not to other major invertebrate groups.

For context, the other options describe groups with different defining traits. Arthropods have an external skeleton (exoskeleton) and jointed limbs; Mollusca typically have a muscular foot, a mantle, and often a shell; Chordata possess a notochord and dorsal nerve cord at some stage. Earthworms and leeches lack these features, which is why they sit in Annelida.