Category
Couplet
Target
1. a. Irregular-shaped body; structure with many pores Porifera
  b. Regular-shaped body (with right and left halves or a cylindrical shape 2
2. a. Radial symmetry (disk-shaped or barrel-shaped) 4
  b. Bilateral symmetry (similar right and left body halves) 3
3. a. Animal has internal skeleton 19
  b. Animal has external skeleton or no apparent skeleton 6
4. a. Body hard, arms extend from a central disk, or spines present 18
  b. Soft body; little or no color 5
5. a. Saucer-shaped transparent body with small tentacles Class Scyphozoa
  b. Barrel-shaped body, tentacles at one end Class Anthozoa
6. a. Hard outer covering 10
  b. No hard outer covering 7
7. a Body flattened

8

  b Body not flattened

9

8. a. Smooth, nonsegmented body Class Trematoda
  b. Apparently segmented, flattened body Class Cestoda
9. a Nonsegmented 11
  b Segemented body Phylum Annelida
10. a. Body has jointed legs 14
  b. Body inside shell is soft, has no jointed legs 13
11. a. Tentacles or other appendages present 12
  b. Body long and tubular, no appendages Phylum Nematoda
12. a. Appears as a snail without a shell Class Gastropoda
  b. Tentacles and eyes present Class Cephalopoda
13. a Bivalved shell (two halves) Class Bivalvia
  b Univalved shell (single unit) Class Gastropoda
14. a. Jointed appendages on most body sections 15
  b. Jointed appendages on certain body segments; not all appendages are legs 16
15. a. One pair of legs per body segment Class Chilopoda
  b. Two pairs of legs per body segment Class Diplopoda
16. a. Two pairs of antennae, large claws often present Class Crustacea
  b. One pair of antennae or none, no large claws 17
17. a. Four pairs of legs, no antennae or wings Class Arachnida
  b. Three pairs of legs, wings present Class Insecta
18. a. Arms present, body surface knobby Class Asteroidea
  b. Many-spined animal, resembles a pincushion Class Echinoidea
19. a. Fishlike, flattened body, appendages finlike not jointed 20
  b. Not fishlike, body not flattened, appendages jointed or absent 21
20. a. Scales on body to not overlap, skeleton of cartilage Class Chondrichthyes
  b. Scales on body overlap, skeleton bony Class Osteichthyes
21. a. Body covered by scales, zero or four legs Class Reptilia
  b. Body not covered by scales 22
22. a. Claws absent Class Amphibia
  b. Claws or nails present on toes, skin covered with feathers or hair 23
23. a Feathered, claws present Class Aves
  b Hair present Class Mammals