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•By far and away, the most successful animal group ever to live •Consists of over 1 million named species, 2 of every 3 animals are arthropods. –Inhabit all ecosystems All have a hard exoskeleton Composed of protein and chitin Allows for great variation in function biological "swiss army knives" Must molt as they grow Limits their size Have well developed body segments and appendages Have well developed sensory organs including true eyes and antennae Have open circulatory systems & special gas exchange organs Divided into 3 classes; Arachnida, Merostomata & Pycnogonida Body divided into 2 regions Abdomen Cephalothorax (fused head & thorax) Lack jaws Have 6 appendages & no antennae First appendages form chilicerae (frequently fangs) Very diverse class Most species parasitic or predatory Many possess book lungs for gas exchange Spiders are able to produce a strong polymer - silk Chilicera in form of fangs Tarantula Black Widow The brown recluse and its bite wounds Dust Mite Common Mite Ancient group of species Changed little over 350 million years Aquatic, mostly found on Atlantic & gulf coasts of United States Class Insecta (insects) Class Chilopoda (Centipedes) Class Diplopoda (Millipedes) Far & away the most diverse of animal groups More types of insects alone than all other animal groups combined Inhabit all terrestrial & freshwater ecosystems. Success largely attributed to coevolution with flowering plants. Insects have 6 legs 3 body parts Head Thorax Abdomen Most insects have wings, however in many species these are vestigial Have advanced excretory system composed of malphygian tubules Exchange gasses through a complex tracheal system Have complex compound eye which is usually extremely sensitive to motion and allows 3600 vision Most insects see well into the UV spectrum Insects usually have specialized jaws/mouthparts suited to their ecological niche Most insects undergo a process of metamorphosis - 2 types Incomplete metamorphosis Larva similar to adult, with differing body proportions Undergoes a series of molts resulting in adult phenotype Larva is very unlike adult phenotype Envelopes self in a coccoon or chrysalis where body breaks-down and reforms into adult form. Millipedes (diplopoda) are segmented worm-like animals Have 2 pairs of legs per segment Primarily herbivores & decomposers Centipedes (Chilopoda) Usually terrestrial carnivores Have 1 pair of antennae Are often poisonous, using modified front claws to immobilize prey Centipede Millipede Includes crabs, lobsters, crayfish, shrimp, krill & barnacles Over 40,000 species Appendages are often highly specialized Gas exchange is usually through gills Many species taste delicious in butter Crayfish Marine Maine Lobster