Arthropods have a unique exoskeleton made of chitin. This shows that arthropods are more closely related to fungi (which also produce chitin) than they are to either cnidarians or lophotrochozoans.

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The presence of chitin in both arthropods and fungi is an example of convergent evolution, not a direct indicator of close evolutionary relationship. Arthropods are more closely related to other animals, including cnidarians and lophotrochozoans, than they are to fungi, as they share a more recent common ancestor with these animals.

Arthropods Have a Unique Exoskeleton Made of Chitin