can you tell me more about the former one?
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" usually hidden entirely under the thorax
Crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( = short, / = tail), usually hidden entirely under the thorax. 
the leaves that form a haven for ant nests are called UNANSWERABLE which family do they belong to? Thamnophilidae where is it normally found? Vast majority of the species are found in the tropics what is their conservative status? 38 species are considered to be near threatened or worse and therefore at risk of extinction what do they feed on? Arthropods which are mostly insects, including grasshoppers and crickets, cockroaches, praying mantises, stick insects and the larvae of butterflies and moths where did the above mentioned name come from? Greek "árthron", "joint", and "pous" (gen. "podos (ποδός)"), i.e. "foot" or "leg", which together mean "jointed leg" what can you tell me about their nervous system? Living arthropods have paired main nerve cords running along their bodies below the gut, and in each segment the cords form a pair of ganglia from which sensory and motor nerves run to other parts of the segment how do they interact with humans? Crustaceans such as crabs, lobsters, crayfish, shrimp, and prawns have long been part of human cuisine but the greatest contribution of arthropods to human food supply is by pollination
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Crab [SEP] Introduction
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( = short, / = tail), usually hidden entirely under the thorax. They live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton, and have a single pair of pincers. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs.