Roundworms and rotifers belong to which phylum?

Roundworms and rotifers are classified in the phylum Aschelminthes, which is known for its diverse group of microscopic and small invertebrates that exhibit bilateral symmetry and have a pseudocoelom. This phylum encompasses several distinct groups, including nematodes (roundworms) and rotifers. Nematodes are characterized by their elongated bodies and are often found in various environments, while rotifers are known for their ciliated crowns and are primarily freshwater organisms.

Mollusca includes a different set of animals, such as snails and clams, which possess a soft body, often covered by a hard shell. Echinodermata is a phylum including sea stars and sea urchins, which are notable for their radial symmetry and unique water vascular system. Arthropoda, which includes insects, arachnids, and crustaceans, is recognized for its jointed limbs and exoskeleton made of chitin.

By understanding the defining characteristics of Aschelminthes and how they relate to both roundworms and rotifers, it becomes clear why this phylum is the correct classification for them.