Which phylum does the roundworm belong to?

The roundworm belongs to the phylum Nematoda, which encompasses a diverse group of worms characterized by their elongated, cylindrical bodies that are typically tapered at both ends. Nematodes are unsegmented and possess a complete digestive system. They are also known for their ecological diversity, thriving in various environments, including soil, freshwater, and marine ecosystems.

Nematoda differentiates itself from other phyla through unique anatomical and biological features. For instance, they have a body covered with a tough cuticle and exhibit a pseudocoelomate body plan, which allows for efficient movement and nutrient transport. These characteristics are crucial for their survival and reproduction.

In contrast, the other phyla mentioned consist of organisms with distinct attributes. Porifera includes sponges that lack true tissues and exhibit a porous structure for filter feeding. Echinodermata encompasses starfish and sea urchins, known for their radial symmetry and water vascular system. Chordata includes vertebrates and some invertebrates that possess a notochord at some stage of development. Understanding these distinctions highlights why Nematoda is the correct classification for roundworms.