Recognize that all organisms are composed of cells and that many organisms are unicellular and must carry out all life functions in one cell. 3.1.6.A5 Describe basic structures that plants and animals have that contribute to their ability to make or find food and reproduce.
Crabs are crustaceans and all crustaceans belong to the taxonomic domain of Eukarya, which are characterised by having cells with nuclei. Eukarya covers all organisms in the Kingdom Animalia, as well as the Kingdoms Plantae, Fungi and Protista.
No, horseshoe crabs are in a class by themselves; they are more closely related to spiders, scorpions, and ticks. They differ from true crabs in that they have no antennae and no mandibles (mouth parts for grinding food). Like spiders, they have a pair of chelicerae (small appendages for moving food into the mouth).