Zoology 10th Edition by Stephen Miller,John Harley

Exercise 16

Members of the subphylum Chelicerata have a body with two tagmata, prosoma, and opisthosoma. They possess chelicerae and pedipalps. The subphylum includes the horseshoe crabs (class Merostomata); scorpions, spiders, harvestmen, mites, and ticks (class Arachnida); and possibly the sea spiders (class Pychnogonida). Most arachnids are predators on other invertebrates or herbivores and harmless to humans. A few spiders, mites, and ticks are either venomous or parasites of humans. The relatively impermeable exoskeleton, efficient excretory structures, internal surfaces for gas exchange, and appendages modified for locomotion on land are adaptations for terrestrial habitats.
Describe arachnid adaptations studied in this section that promote life apart from standing water.