Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A field class records the symmetry of the animals in a rock pool.
| Symmetry | Animals |
|---|---|
| radial | |
| bilateral | |
| asymmetrical |
Levels of organisation: cellular (Porifera), tissue (coelenterates), organ (Platyhelminthes), organ system (annelids, arthropods, molluscs, echinoderms, chordates). An incomplete gut has one opening; a complete gut has a mouth and an anus. Open circulation bathes the tissues in blood (arthropods, molluscs); closed circulation keeps it in vessels (annelids, chordates). Symmetry: asymmetrical, radial or bilateral.
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. Total. animals.
Step 2. Per cent. .
Step 3. Asymmetrical. Most sponges are asymmetrical, so these are most likely sponges.
Answer: animals; bilateral; sponges.
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