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The Class Arachnida - containing venom Ticks shown in...

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The Class Arachnida The class Arachnida includes over 60,000 described species (and most likely a very large number of as yet undescribed ones) of spiders (around 35,000 species), mites and ticks (25,000 species), scorpions (1200 species), and other forms. Nearly all arachnids are terrestrial. Arachnids have a cephalothorax covered with a carapace-like shield. The abdomen may be segmented or unsegmented. Appendages on the abdomen are absent or modified, for example forming the spinnerets of spiders. Respiration is via tracheae or book lungs. Scorpions are arachnids. They are the oldest terrestrial arthropods known from fossils. All scorpions are nocturnal and spend most of the day hidden under a log or rock. Their pedipalps are large pincerlike appendages, and their abdomen ends in a stinger
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Unformatted text preview: containing venom. Ticks, shown in Figure 17, are parasites that suck blood and sometimes transmit diseases. Chiggers are larvae of certain mites and feed on the skin of vertebrates. Spiders, shown in Figure 18, have a narrow waist separating the cephalothorax from the abdomen. Spiders have numerous simple eyes rather than compound eyes. The chelicerae are modified as fangs with ducts from poison glands. The abdomen has silk glands used to spin a web to trap prey. Invaginations of the body wall form lamellae (pages) of the book lungs; air flows across the lamellae in the opposite direction from blood flow to exchange gases more efficiently....
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The Class Arachnida - containing venom Ticks shown in...

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