Biological classification is the scientific way biologists group and categorize extinct and living species of organisms. Order is a component of classification and a good starting place in understanding the vast variations in structure, habitation and life of the wondrous world of sharks.
A problem with gathering information on sharks is that they are cartilaginous, without rib cages, with very little if any bone in their bodies. So there aren't any fossilized bony skeletons with rib cages to analyze. Only shark teeth survive, or a few fossilized impressions.
General Shark Biological Classification Features:
- Sharks have 5,6,or 7 pair of gill openings. - Only a total of 7 shark species out of over 450 species have 6 or 7 pair of gill openings, and they are not in the New England area. All sharks in New England will have: 5 pair of gill openingsThese gill openings will be located on the sides of the head (The flat bottom dwelling angel shark is an exception.)
- Rough sand papery skin (especially when rubbed from tail to head.) This roughness is caused by small tooth like scales called dermal denticles. (also called placoid scales or skin teeth.)The dermal denticles on a shark will not be transparent and flaky as they are on many fish. In the magnified image you can see the denticles on the sharks skin. On some species the scales overlap, on others they do not overlap. Not all sharks have eye protection called nictitating membranes.
- Of the 453 shark species worldwide, there are about 15 species that lack this eye protection.
- Upper jaw protrusion is a prominent component of the feeding mechanism in most elasmobranchs and has received considerable attention over the years. In this paper, we review what is known of muscle activity during prey capture in elasmobranchs, particularly that of upper jaw protrusion, and evaluate the extent to which functional modifications have evolved through changes in anatomy or patterns of muscle activity. To date, motor activity during feeding has been documented in only four species of elasmobranchs, although they represent the three major elasmobranch groups: Galea (typical sharks); Squalea (dogfish sharks); and Batoidea (skates and rays). Our efforts show that while muscles involved in cranial elevation and lower jaw depression and elevation show a conserved pattern of motor activity and function across species, other muscles show a more variable history. Our observations of elasmobranch upper jaw protrusion mechanisms suggest a mosaic of character changes over the course of evolution that involve anatomical changes in all cases and modifications of muscle activation patterns in some cases. During the evolution of feeding mechanisms of elasmobranchs, there have been two structural changes incorporating a pre-existing motor pattern to yield an unmodified kinematics profile, the original preorbitalis and the descendent preorbitalis. One additional instance of structural modification is accompanied by an alteration in the motor pattern leading to a change in movement. In biology, a trait or character is a genetically inherited feature of an organism.
The eight shark orders listed below are a general overview of characteristics of each order and the sharks that belong to that order.
- Body flattened, raylike mouth terminal: bramble shark; dog shark; rough sharks and prickly sharks.
- No anal fin, snout elongated, sawlike: saw shark.
- 6 or 7 gill slits, one dorsal fin: cow shark and frilled shark
- Anal fin present, nictitating eyelids; spiral intestinal valve; mouth behind front eyes: ground shark; blue; tiger; bull; reef; oceanic whitetip; catshark; hammerhead; hound shark.
- No nictitating eyelids; ring intestinal valve; no fin spines: goblin shark; basking shark; megamouth shark; thresher shark; short fin; longfin and great white.
- Mouth well in front of eyes; 5 gill slits; 2 dorsal fins: carpet shark; zebra shark; nurse shark; wobbegong and whale shark.
- Dorsal fin spine: bullhead ; horn shark.
- two dorsal fins, no anal fin ,no nictitating membrane, five gill slits. bramble shark, gulper shark, sleeper shark, dog fish shark