Pagurus Usually, a few new species are discovered each year. The following list is current : The following are all "nomina nuda". They have never been validly described as new species, but only mentioned under these names: Pagurus Pagurus is a genus of hermit crabs in the family Paguridae. Like other hermit crabs, their abdomen is not calcified and they use snail shells as portable homes. These marine decapod crustaceans are omnivorous, but mostly prey on small animals and scavenge carrion. "Trigonocheirus" and "Pagurixus" used to be considered subgenera of "Pagurus", but the former is nowadays included in "Orthopagurus", while the
History of manifolds and varieties History of manifolds and varieties The study of manifolds combines many important areas of mathematics: it generalizes concepts such as curves and surfaces as well as ideas from linear algebra and topology. Certain special classes of manifolds also have additional algebraic structure; they may behave like groups, for instance. In that case, they are called Lie Groups. Alternatively, they may be described by polynomial equations, in which case they are called algebraic varieties, and if they additionally carry a group structure, they are called algebraic groups. The term "manifold" comes from German "Mannigfaltigkeit," by Riemann. In English, "manifold" refers to