(See attached file for full problem description)
In the animal kingdom, you can place animals in categories based on certain differences in the characteristics that each possesses. If you know what critical traits to look for, it is possible to separate any animal into its proper taxonomic category. Use this dichotomous key to help determine the taxonomic category to which a specific organism belongs.
For example, for Organism 1, you would proceed like this:
1b: Regular-shaped body (with right and left halves or a cylindrical shape
2a: Radial symmetry (disk-shaped or barrel-shaped)
4a: Body hard, arms extend from a central disk, or spines present
18a: Arms present, body surface knobby
Therefore, it belongs to Class Asteroidea.
For Organism 2, you would ...