75% of all organisms are arthropods, mostly insects. Includes spiders, centipedes, and crustaceans. Arthropods have exoskeletons. Mollusks and sponges have exoskeletons.
Insects are the biggest arthropod group. They have chitin exoskeletons that protect and support the head, thorax, and abdomen.
Arthropods comprise the phylum arachnida, which includes spiders. Besides spiders, ticks, mites, chiggers, and scorpions are other common arachnids.
Crustaceans are ocean-dwelling arthropods with rigid exoskeletons. Some, like the crayfish, live in freshwater, while others, like the Coconut crab, live on land.
Strong exoskeletons defend millipedes from predators. They curl to look less beautiful and protect their bottom. Some millipedes emit poison to ward off predators.
Centipedes have millipede-like exoskeletons. Centipedes use venom to kill prey, but not humans. The Asian Forest Centipede bite causes discomfort and edoema.
The shelled mollusks with exoskeletons are gastropods and cephalopods. Snails are gastropods, clams and oysters are cephalopods.
Both mollusc types have exoskeletons. Their shells are both houses and predator defence. Compared to arthropods, mollusks have calcium-based exoskeletons.