Interactive exercise. Assistance may be required. Use the dichotomous key below to identify the following arachnids, invertebrates with eight legs. Click on each sketch to see a more detailed image.

Follow these guidelines when using a dichotomous key.

  1. Identify the unknown objects one at a time.
  2. Start at step one and progress through the steps, as indicated by the key, until the unknown object has been identified.
  3. Select another unknown object and start back at step one. Never start in the middle of the key.

1. a. Arachnid as a tail or a stinger. Go to #2
b. Arachnid has no tail or stinger. Go to #3
2. a. Tail is straight (does not curve upward) like a needle. Order Uropygi
b. Tail curves upward with a stinger at the tip. Order Scorpiones
3. a. Has enlarged pedipalps (claws). Go to #4
b. Lacks enlarged pedipalps (claws). Go to #5
4. a. Body is less than 5mm long and flat. Order Pseudoscorpiones
b. Body is 8 to 51mm long and spider-like. Order Amblypygi
5. a. Arachnid has regular legs. Goo to #6
b. Arachnid legs are thin/stilt-like with "high" knees and body low to ground. Order Opiliones
6. a. Body is separated into a cephalothorax and abdomen (i.e. has a waist). Go to #7
b. Body is oval-shaped and lacks a waist. Order Acari
7. a. Has seven segments on each leg and one pair of legs is not longer than rest. Order Araneae
b. Has some other number of segments on each leg and one pair of legs are longer than the rest. Order Solifugae

Sources for images used in the interactive, as they appear, top to bottom: