What describes phylum Annelida?

Phylum Annelida is characterized by animals that are long, round, and segmented. This distinctive segmentation is a key feature of annelids, which includes worms such as earthworms and leeches. The segmentation allows for greater flexibility and mobility, as each segment can move independently of the others, aiding in burrowing and locomotion.

Annelids possess a coelom, or body cavity, which is divided into segments, each often containing its own set of organs. This segmentation also contributes to their body plan, which typically is elongated and cylindrical. Overall, this unique structure is fundamental to their anatomy and contributes significantly to their adaptability to different environments.

While some annelids do inhabit aquatic environments, not all do, as there are many terrestrial species as well. The other characteristics mentioned in the other choices do not specifically align with the defining features of annelids. Their soft-bodied nature is common among numerous invertebrate groups, and the organization of cells into specialized tissues is a feature of many animal phyla, not unique to Annelida.