Final answer:
Crustaceans, such as crabs, lobsters, shrimp, and krill, are characterized by a hard exoskeleton, segmented bodies, and jointed limbs. They have a diverse range of diets and reproductive strategies, and even include terrestrial species like the pill bug. The carapace is a protective plate that covers the cephalothorax of many crustaceans.
Step-by-step explanation:
Crustaceans are a diverse group of aquatic arthropods and include well-known species such as crabs, lobsters, shrimp, and krill. They are significant for various ecosystems and serve as an important food source for humans and other larger marine animals. Crustaceans are characterized by their segmented bodies with jointed appendages and a hard exoskeleton. The exoskeleton is often infused with calcium carbonate for added strength. Crustaceans, which can be both freshwater and marine, have an estimated 70,000 marine species and a smaller number of terrestrial species, such as the pill bug.
The carapace is a protective plate that covers the cephalothorax of many crustaceans. They have an open circulatory system, with blood pumped by a dorsal heart. Reproduction varies across different crustacean species, with most employing separate sexes and sexual reproduction, although hermaphroditism and serial hermaphroditism are present in some species. Their diets can range from carnivorous to herbivorous, detritivorous, and even parasitic or cannibalistic behaviors under certain conditions.