Which two animal groups are classified as ecdysozoans?

• A. Cnidarians and Echinoderms
• B. Chordates and Platyhelminthes
• C. Arthropods and Nematodes
• D. Mollusks and Annelids

Answer: (C)

Verified step by step guidance

1. Understand the term 'Ecdysozoans': Ecdysozoans are a group of protostome animals characterized by their ability to molt (shed their exoskeleton or outer covering) through a process called ecdysis. This is a key feature that distinguishes them from other animal groups.
2. Review the major animal groups listed in the problem: Cnidarians, Echinoderms, Chordates, Platyhelminthes, Arthropods, Nematodes, Mollusks, and Annelids. Identify which of these groups exhibit molting (ecdysis).
3. Recall that Arthropods (e.g., insects, spiders, crustaceans) and Nematodes (roundworms) are the two groups that undergo ecdysis. This is a defining characteristic of ecdysozoans.
4. Eliminate the other options: Cnidarians and Echinoderms do not molt; they belong to different clades. Chordates and Platyhelminthes also do not exhibit ecdysis. Mollusks and Annelids grow continuously without molting, so they are not ecdysozoans.
5. Conclude that the correct classification of ecdysozoans includes Arthropods and Nematodes, as they share the defining trait of molting their exoskeleton or outer covering.