Sharks are generally divided into 8 groups.These are further subdivided into  families,with a variable number of species in each.The following description are based largely on external features.
The sevengill shark
Frilled and Sixgill and sevengill Sharks (order Hexanchiformes)
Comprising of 2 families,these sharks have 6 or 7 pairs of gill opening (most sharks have 5) ,an anal fin and a single spineless dorsal fin.They are wide ranging and is found in deep waters.Frilled sharks  belongs to family Chlamydoselachidae and sxgill and sevengill shark belongs to family Hexanchidae.
Dogfish Sharks(order Squaliformes)
The seven families in this order have 2 dorsal fins (either spined or spineless),no anal fin,a short to moderately long conical snout,and 5 pairs of gill opening.Most dogfish occur in deep water on slope of continents and islands,but some occur in temperate inshore waters and as far as the arctic and Antarctic.Bramble sharks belongs to family Echiorhinidae ,dogfish sharks to Squalidae,Gulper sharks to family Centrophoridae,Lanternsharks to Etmopteridae,,sleeper sharks to family Somniosidae,Roughsharks to Oxynotidae and Kitefin Sharks to Dalatiidae.There are at least nine species,including cookiecutter shark and one of the world smallest sharks,the spined pygmy shark.
A school of spiny dogfish shark
The Japanese Sawshark
SawSharks(order Pristiophoriformes)
There is one family,Pristiophoridae,of these small to moderate sized,elongated,flat-headed sharks.Believed to be the closest living relatives of the rays,thoer most distinctive features is a long saw like snout with 2 long barbels,2 spineless dorsal fins,no anal fins,and 5-6 pairs of gill opening.There are more than 5 species,occuring from shallow to deep waters on the shelves and slopes of the western north atlantic,Indian,and Pacific ocean.
AngelSharks(order Squatiniformes)
These comprise a single family (squatinidae) of moderate sized,highly flattened sharks.While ray like in appearance,They have 2 small spinless dorsal fins,no anal fins,a short truncated snout with a mouth at the tip,5 pairs of gill opening,and huge pectoral fins with angular extensions covering the gill opening.Most of the more than 15 species occur inshore in temperate waters,with a few found in deep tropical waters.
The Angelshark