Crustaceans
Crustaceans are marine invertebrate animals characterized by a hard exoskeleton composed of chitin and calcium carbonate, segmented bodies, and multiple pairs of jointed legs. They form a diverse group, with over 67,000 known species, making up around 10% of all known animal species. Crustaceans can be found in various marine habitats, from the deep sea to shallow coastal waters, as well as in freshwater and terrestrial environments. Crustacean bodies typically consist of two main parts: the cephalothorax (fused head and thorax) and the abdomen. The cephalothorax bears sensory organs such as eyes, antennae, and mouthparts, while the abdomen contains the reproductive and respiratory structures. Crustaceans have a complex life cycle involving larval stages and molting to grow new exoskeletons. Crustaceans play essential roles in marine ecosystems as scavengers, filter-feeders, and predators. They serve as both primary and secondary consumers, contributing to the food chain's intricate web. Some notable crustacean examples include crabs, lobsters, shrimps, crayfish, barnacles, and krill. These creatures have cultural, economic, and ecological significance, making them a crucial area of study in marine biology and conservation efforts.