Biology/Dichotomous Key

Couplet Number Statement Choices Classification

1 a. Symmetry is irregular (neither bilateral or radial); aquatic; body structure without tissues or organs Class Demospongiae

b. Symmetry is radial or bilateral 2

2 a. Radial symmetry, lacks a well defined head 3

b. Bilateral symmetry (similar right and left body halves, anterior head end and posterior tail end) 6

3 a. No spines or arms present 4

b. Spines or arms present 5

4 a. Barrel-shaped body, short tentacles at one end surrounding mouth, adults attached to a substrate Class Anthozoa

b. Saucer-shaped, transparent body with thin tentacles, free floating Class Scyphozoa

5 a. Five arms present, body surface knobby Class Asteroidea

b. Many-spined animal, resembles a pincushion Class Echinoidea

6 a. Animal has no apparent skeleton, or may have an exoskeleton (hard outer covering), or may have a shell; invertebrate 7

b. Animal has internal skeleton; vertebrate 16

7 a. No hard outer covering, no exoskeleton, or no shell; worm-like 8

b. Hard outer covering, exoskeleton, or shell; not worm-like 11

8 a. Body is segmented Class Clitellata

b. Body is not segmented 9

9 a. Body long and tubular Class Secernentea

b. Body flattened 10

10 a. Free living, aquatic, ribbon-like, smooth Class Turbellaria

b. Endoparasites (live inside host); may look segmented Class Cestoda

11 a. No jointed appendages 12

b. Jointed appendages 14

12 a. Soft body inside bivalve shell (hinged shell with 2 halves), no head Class Bivalvia

b. Soft body, obvious head 13

13 a. May or may not have a shell; head with tentacles, small eye or eye spot Class Gastropoda

b. Large head with tentacles and large eyes present Class Cephalopoda

14 a. Two pairs of antennae, large claws often present Class Crustacea

b. One pair of antennae or none, no large claws 15

15 a. Four pairs of legs, no antennae or wings Class Arachnida

b. Three pairs of legs, wings present Class...