Chondrichtyes They are cartilaginous Fishes Jawed Fishes Paired Fins Paired NaresSharks, Skates, Rays amd Chimaeras
Chondrichtyes Elasmobranchii (sharks, rays and skates) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class).
Skeleton The skeleton is cartilaginous. The notochord, which is present in the young, is gradually replaced by cartilage. They lack ribs, so if they leave water, the larger species own body weight would crush their internal organs long before they suffocate.
As they do not have bone marrow, red blood cells are produced in the spleen and the epigonal organ (special tissue around the gonads, which is also thought to play a role in the immune system). They are also produced in the Leydigs organ which is only found in cartilaginous fishes, although some do not possess it. The subclass Holocephali, which is a very specialized group, lacks both the Leydigs and epigonal organ.
Appendages Tough skin is covered with dermal teeth also called placoid scales or dermal denticles, making it feel like sandpaper. In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction and very rough if rubbed in the other. Another exception are the electric rays, which have a thick and flabby body, with soft, loose skin devoid of dermal denticles and thorns.
Originally the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid and pubioischiadic bars evolved. In rays, the pectoral fins have connected to the head and are very flexible. One of the primary characteristics present in most sharks is the heterocercal tail, which aids in locomotion.
Respiration All Chondrichthyes breathe through 5-7 gills, depending on the species. A spiracle is a small hole found behind each eye. These can be tiny and circular.
Functions Eyes well-adapted to the marine environment tapetum lucidum - allows them to contract and dilate their pupils - Located behind the retina, reflects light back to it, increasing visibility in darkness Some species have nictitating membranes for eye protection, some roll their eyes back to protect them while striking prey
Nostril Very keen olfactory senses Some species can detect as little as 1 ppm of blood in seawater Can determine direction of a given smell through timing of scent detection
Spiracle Provides oxygenated water directly to the eye and brain through a separate blood vessel Allows breathing even when buried or lying at the bottom of the ocean Vestigial/not present in larger, faster moving sharks, present in bottom-dwelling sharks
Respiration Extracts oxygen as water passes through its gills While sharks move, water passes through the gills and mouth Some sharks have lost the ability to pump water through their gills and must move continuously
Gills Usually 5-7 pairs of slits present at the sides of their heads No gill covers Filter-feeding sharks expell water through their gills
Mouth Have different kinds of teeth according to diet Crustaceans feeders have flat teeth for crushing Fish feeders have triangular upper teeth for cutting and pointed lower teeth for gripping Plankton feeders have teeth for filtering, or reduced teeth Teeth are arranged in multiple lines in a row
Presence of a tongue-like structure called the basihyal – a thick, cartilaginous structure on the floor of the mouth Useless for most sharks
Snout Cartilaginous and spongy, to resist impact caused by chasing after prey
External Featuresof a Dog Shark Lateral line canal Fin Spine Pectoral Fin Pelvic Fin
Lateral line canal is a series of fluid-filled canals just below the skin of the head and along the sides of the body Contains a number of sensory cell called the neuromasts detecting low-frequency vibrations and directional water flow. The shark can sense frequencies in the range of 25 to 50 Hz.
Fin Spines adaptation for defense against predators. carry a poison secreted by glands at their base
Pectoral fin located behind the sharks head. extend outward, act like an airplanes wings to provide the shark with lift and function as a steering mechanism during swimming and to keep the shark from sinking
Pelvic fin also act as stabilizers. Located between the pectoral and anal fins Male sharks have modified pelvic fins called claspers. have a secondary purpose in males for clasping during mating.