Which phylum includes segmented worms like earthworms?

The phylum that includes segmented worms, such as earthworms, is Annelida. Members of this phylum are characterized by their body structure, which is divided into segments or "metameres." This segmentation allows for greater flexibility and mobility, making annelids well-adapted to a variety of environments, including terrestrial habitats like soil.

Annelids have a coelom, which is a body cavity that is fully lined with mesoderm, and they feature a complex organ system, including a closed circulatory system. This complexity enables them to perform various functions efficiently, such as movement and nutrient absorption.

In contrast, other phyla like Mollusca (which includes snails and octopuses), Arthropoda (which includes insects and crustaceans), and Nematoda (which includes roundworms) do not have the distinct segmented body plan found in Annelida. Therefore, the characteristics and biological organization of segmented worms very clearly place them within the Annelida phylum.