Short answers, pulled from the story.
Arthropods account for over 80 percent of all known living animal species. This group represents the most successful animal classification on Earth. Their diversity spans from microscopic mites to the Japanese spider crab with legs spanning up to 13 feet.
The phylum Arthropoda has thrived for over 500 million years. Fossil evidence from the Cambrian period, such as the Burgess Shale, reveals a diverse array of early forms. This evolutionary history includes the development of segmented bodies and jointed appendages.
Moulting is responsible for 80 to 90 percent of all arthropod deaths. This dangerous process leaves the animal vulnerable and nearly immobilized while the new shell hardens. The cycle involves shedding the old exoskeleton to allow for growth and development.
Arthropods have an open circulatory system where blood flows freely through a body cavity called the haemocoel. This blood, known as haemolymph, is pumped by a muscular tube running along the back of the animal. Oxygen transport varies by species, using respiratory pigments or simple diffusion through the body surface.
Most arthropods possess compound eyes made of hundreds or thousands of individual lenses called ommatidia. They also utilize setae as touch sensors and chemical sensors to taste and smell. Pressure sensors function as eardrums to detect sound waves while statocysts provide information about balance and acceleration.
Arthropods provide food sources like crabs, lobsters, and shrimp, as well as sustainable protein from insects. The red dye cochineal was economically important to the Aztecs and Mayans, and shellac is used in woodworking and as a food additive. The blood of horseshoe crabs contains a clotting agent used to test antibiotics and detect spinal meningitis.