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Arthropods Name: _________________________________________ Class:__________ Date: ____________ Vocabulary Term Definition arthropods Invertebrate animals with jointed limbs, a segmented body, and an exoskeleton made of chitin. hemolymph Blood-like circulatory fluid of some invertebrates. molting Shedding of the old shell to make way for a new growth. What does this lobster have in common with a wasp? You might notice that their bodies have segments. And they both have a hard outer layer. Because they share these and other features, they are both classified as arthropods. What are Arthropods? How often do you think you see an arthropod? Well, have you ever looked up close at an ant? A spider? A fly? A moth? With over a million described species (and many more yet to be described) in the phylum containing arthropods, chances are, you encounter one of these organisms every day, without even leaving your house. Arthropods are a very diverse group of animals. In fact, they are the biggest group of animals on the planet, with upwards of 5 million distinct species. Types of Arthropods Arthropods belong to the phylum Arthropoda, which means “jointed feet,” and includes four living subphyla. • Chelicerata, which includes spiders, mites, and scorpions. In these animals, the first pair of appendages are often modified as fangs or pincers, and are used to manipulate food. Spiders have eight legs. • Myriapoda, which includes centipedes and millipedes. All of these animals live on land, and can have anywhere from ten to nearly 200 pairs of appendages. • Hexapoda, which includes the insects. These animals dominate the land. All hexapods have three pairs (six appendages) of walking appendages. • Crustacea, which includes lobsters, crabs, barnacles, crayfish, and shrimp. These animals dominate the ocean, and usually have a set of anterior appendages that are modified as mandibles, which function in grasping, biting, and chewing food. Characteristics of Arthropods Characteristics of arthropods include: 1. A segmented body with a head, a thorax, and abdomen segments. 2. Appendages on at least one segment. They can be used for feeding, sensory reception, defense, and locomotion. In addition to legs, antennas and mouth parts are considered modified appendages. 3. A nervous system. 4. A hard exoskeleton made of chitin, which gives them physical protection and resistance to drying out. In order to grow, arthropods shed this outer covering in a process called molting.
