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Phylum Arthropoda The largest group of animals within this kingdom • Arthropods are the most biologically successful group • 1 million known species of arthropods • They are suited for life in most conditions Division of Arthropoda • The phylum arthropoda can be divided into five groups, or subphylum: – – – – – Crustaceans Centipedes Millipedes Arachnids Insects They All Share Certain Characteristics . . . • • • • • Bilateral Symmetry Coelomates Segmented body Organ / system level of organization Complete digestive tract What Separates Them From Other Animals?? • Jointed appendages • Exoskeleton • Chitin and protein • Well-developed nervous system • Distinct brain, nerve cords • Open circulatory system • Tubular heart and arteries Jointed appendages • Legs are made up of several pieces • These pieces are connected at hinged joints • Different arrangements of these joints along with opposing sets of muscles allow different functions Arthropoda = “jointed feet” The Exoskeleton • Composed of protein and chitin, a carbohydrate • Provides protection to the soft body parts • Prevents water loss • Adaptation to life on land • Exoskeletons do not grow along with the organism » Molting – shedding of the exoskeleton, replacement with larger one Arthropods Are Segmented . . . • Segments are modified and fused • Form specific body regions – HEAD • Six segments • Contains specialized mouth • Antennae • Compound eyes – THORAX • The middle region – ABDOMEN • The posterior region Advancements in the Nervous System • Cephalization is extensive – Disinct anterior region – Most sensory organs located in anterior region • Well-developed sensory organs – Eyes – Receptors for smell – Antennae to respond to touch All Arthropods Have an Open Circulatory System • Tubular heart located dorsally – Above digestive tract • Transport medium called hemolymph • Arteries carry hemolymph away from heart – Flow into spaces surrounding tissues and organs • Hemolymph brought back to the heart through pores equipped with valves Arthropoda : Reviewing Their Success • Their success has been brought about by several evolutionary events – Exoskeleton acting as a cuticle – Segmentation and appendages – Extensive nervous system and behaviors
