Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Use the key to the phyla for three unknown animals.
Metameric segmentation: the body is divided outside and inside into segments, with some organs repeated (annelids, arthropods, chordates). The notochord is a rod formed from mesoderm on the dorsal side of the embryo; chordates have it. Key: cellular level, Porifera; radial and diploblastic, Coelenterata or Ctenophora; bilateral and triploblastic: no cavity, Platyhelminthes; pseudocoelom, Aschelminthes; coelom, Annelida to Chordata.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. X. Radial and diploblastic: Coelenterata or Ctenophora.
Step 2. Y. Bilateral with a pseudocoelom: Aschelminthes.
Step 3. Z. A coelomate with a notochord: Chordata.
Answer: X Coelenterata or Ctenophora; Y Aschelminthes; Z Chordata.
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