This order represents the second largest order and includes 7 families and about 113 species and their most distinguishing feature is the lack of an anal fin. Most species also have a spine in front of the first dorsal fin. The majority are deep water species, and some have luminescent organs. Certain species can reach large sizes for instance the greenland shark, Somniosus microcephalus, with 7 m. Scientists assume that the most abundant species of all known sharks may be the spiny dogfish, (Squalus acanthias), the main species used for "fish & chips".