Brachyurids

Brachyurids are a infraorder of true crabs, a group of crustaceans belonging to the order Decapoda, which also includes shrimp, lobsters, and crayfish. The defining characteristic of brachyurids is their greatly reduced and flattened abdomen, which is tucked tightly beneath the cephalothorax. This characteristic gives them their common name, "short-tailed" crabs. Unlike lobsters and shrimp, brachyurids lack a distinct tail. Their carapace, or shell, is typically broad and flattened, and their first pair of legs is modified into large, powerful pincers, or chelipeds.

Brachyurids are found in marine, freshwater, and terrestrial environments worldwide, inhabiting a vast range of habitats from shallow coastal waters and coral reefs to deep-sea trenches and tropical forests. They are incredibly diverse, with over 6,700 described species. This diversity is reflected in their varied sizes, shapes, colors, and behaviors. Some brachyurids are scavengers, feeding on dead organic matter, while others are predators, hunting small invertebrates and fish. Many are also omnivores, consuming a mix of plant and animal material. Their life cycle typically involves a larval stage, often planktonic, before metamorphosing into a juvenile crab.

The ecological roles of brachyurids are significant. They are important components of food webs, serving as both prey for larger animals and predators of smaller organisms. Their burrowing activities can influence sediment composition and nutrient cycling in benthic environments. Humans utilize brachyurids as a food source, with many species being commercially harvested. They are also subjects of scientific study, providing insights into evolution, ecology, and behavior.