Problem 1

"An organism has radial symmetry, is diploblastic, has cnidocytes on its tentacles, and alternates between polyp and medusa forms. Identify its phylum and give two examples."

Solution: Step 1: Radial symmetry → candidates: Cnidaria, Ctenophora, adult Echinodermata Step 2: Diploblastic → eliminates adult Echinodermata (triploblastic) Step 3: Cnidocytes → EXCLUSIVELY Cnidaria; eliminates Ctenophora (no cnidocytes) Step 4: Polyp-medusa alternation → confirms Cnidaria (metagenesis) Answer: Phylum Cnidaria. Examples: Obelia (shows full metagenesis), Aurelia (primarily medusa)