BACKGROUND:

Arthropods are bilaterally symmetrical and have jointed body segments with a pair of appendages attached to each body segment. The body is covered with a cuticle (thickened substance) which comes off ("molts") when the arthropod gets larger. There is no internal skeleton. Their circulatory system is very simple and they reproduce by laying eggs.

Identification of arthropods is not easy, because there are so many "creepy crawlies" out there. Below is  information that may help you group arthropods for your students. You may want to use other books or information on the internet to help identify the different arthropods. 

Spiders, scorpions, ticks, and horseshoe crabs belong to a group called the chelicerates. They have no antennae and the first pair of appendages are pincher-like. 

The arthropods called mandibulates are characterized by their head appendages and include most of the common  arthropods. We will be concentrating on the more common insect and crustacean groups.  A head (a), thorax (b), abdomen (c), wing cover or elytra (d), wing (e) and antennae (f)  are usually present.  Crustaceans, such as brine shrimp, are predominantly aquatic and have gills for respiration.

PROCEDURE:

1. Give students a worksheet and bag of plastic insects. Instruct the students to  try and find their name (order level). On the worksheet students should describe the head, the body (thorax and abdomen), and appendages (legs).  You may want them draw the specimen on the back of the sheet to help them look at the various parts.   The important objective is to observe the different types of arthropods. 
     
   Identification of insects on worksheet: Order Odonata  Damselfly (right), dragonfly (left);  Order Orthoptera Grasshopper (right),  Katydid (left);  Order Hemiptera Bug (right);  Stink bug (left);  Order Homoptera Cicada (right);  leafhopper (left); Order Coleoptera  firefly (right);  ladybug (left); Order Diptera  fly (right);  mosquito (left);  Order Lepidoptera butterfly (right);  moth (left);  Order Hymertoptera bee (right);  wasp (left).
     
2. Insects are some of the most successful land organisms. Insects bite humans, irritate skin, and sometimes cause disease. The insect body is composed of a head, thorax, and on abdomen with 6 legs. The head has a pair of compound eyes.
     
3. Pass the horseshoe crab, and ask students if this belongs to the arthropods. Horseshoe crabs are marine organisms that belong to the crustacea group, which is a subgroup of arthropods.
     
4. Students should look at the crabs and count the legs. Crabs are also an arthropod.
     
5. Brine shrimp are an effective way to look at arthropods. You can purchase them at most pet stores. They are sometimes called "sea monkeys."  Brine shrimp are used to feed larger fish. We suggest using a petri dish or other see through container and look at them with the Swift GH microscope.
     
   Brine shrimp belong to the genus Artemia and are one of many small crustaceans of the order Anostraca (class Branchiopoda) inhabiting brine pools and other highly saline inland waters throughout the world. Young brine shrimp hatched there from dried eggs are used widely as food for fish and other small animals in aquariums. Measuring up to 15 mm (0.6 inch) in length, the body of the brine shrimp has a discrete head with a large eye and stalked compound eyes, a thorax bearing a series of limbs, and a slender abdomen without appendages. Brine shrimp normally swim in an upside down position by rhythmically beating their legs. They feed primarily on green algae, which they filter from the water with their legs
     
6. As the students are looking under the microscope make sure you direct their observations by comparing, contrasting, and counting all segments.