Class CHONDRICHTHYES
This class consists of a group of cartilaginous fish such as sharks, skates, rays and chimaeras.
ECOLOGICAL ROLE
Chondrichthyans are usually at the top of the food chain and are apex predators. They are responsible for predating on animals to maintain a controlled population, thus keeping the ecosystem stable and balanced. The absence of chondrichthyans could cause the whole food chain or food web to collapse.
Chondrichthyans are usually at the top of the food chain and are apex predators. They are responsible for predating on animals to maintain a controlled population, thus keeping the ecosystem stable and balanced. The absence of chondrichthyans could cause the whole food chain or food web to collapse.
MOVEMENT STRUCTURES/TYPE
Chondrichthyes sharks swim by moving their heads and tails from side to side in the water. They use fins to stabilize themselves when they swim, to steer themselves in the water, or to propel themselves through the water. The bodies of shark species are shaped for hydrodynamic efficiency, where swimming is achieved by side to side undulations of the tail. In rays, the body is flattened from the top and bottom, the tail is reduced in size, and movement through the water is achieved by undulation of the tips of the pectoral fins. Chimaeras move by rapid movement of the pectoral fins, or by slow lateral movements of their tails. To aid in movement for some Chondrichthyan groups, their skin is covered with small teeth-like structures called dermal denticles. These structures are designed to reduce the amount of drag while swimming, making travelling through the water more efficient.
Chondrichthyes sharks swim by moving their heads and tails from side to side in the water. They use fins to stabilize themselves when they swim, to steer themselves in the water, or to propel themselves through the water. The bodies of shark species are shaped for hydrodynamic efficiency, where swimming is achieved by side to side undulations of the tail. In rays, the body is flattened from the top and bottom, the tail is reduced in size, and movement through the water is achieved by undulation of the tips of the pectoral fins. Chimaeras move by rapid movement of the pectoral fins, or by slow lateral movements of their tails. To aid in movement for some Chondrichthyan groups, their skin is covered with small teeth-like structures called dermal denticles. These structures are designed to reduce the amount of drag while swimming, making travelling through the water more efficient.
BODY COVERING; CELL LAYERS; LEVEL OF ORGANIZATION; PROTECTION
Chondrichthyes are jawed vertebrates with paired fins, paired nostril openings, scales, and a heart with its chambers in series. Chondrichthyans, for the most part, have tough skin covered with dermal teeth. In most species, all dermal denticle are situated in one direction, making the skin feel very smoothed if rubbed in one direction and very rough if rubbed the other. The basic body plan of Chondrichthyans includes a skull, jaws, teeth, a backbone, fins, but lack ribs. Chondrichthyans have three types of unpaired fins - dorsal, caudal, and anal, and two types of paired fins - pectoral and pelvic.
Chondrichthyes are jawed vertebrates with paired fins, paired nostril openings, scales, and a heart with its chambers in series. Chondrichthyans, for the most part, have tough skin covered with dermal teeth. In most species, all dermal denticle are situated in one direction, making the skin feel very smoothed if rubbed in one direction and very rough if rubbed the other. The basic body plan of Chondrichthyans includes a skull, jaws, teeth, a backbone, fins, but lack ribs. Chondrichthyans have three types of unpaired fins - dorsal, caudal, and anal, and two types of paired fins - pectoral and pelvic.
SUPPORT
Members of the Chondrichthyes all lack true bone and have a skeleton made of cartilage. Chondrichthyans lack ribs and bone marrow. The chondrichthyan body is supported by a long fibrous rod (notochord), around which lie a series of cartilaginous vertebral elements. Sharks lack a swim bladder, which is a gas-filled buoyancy control organ found in many fish. Their light skeleton and oil-filled liver helps reduce its overall density, thus allowing it to ascend and descend in the water.
Members of the Chondrichthyes all lack true bone and have a skeleton made of cartilage. Chondrichthyans lack ribs and bone marrow. The chondrichthyan body is supported by a long fibrous rod (notochord), around which lie a series of cartilaginous vertebral elements. Sharks lack a swim bladder, which is a gas-filled buoyancy control organ found in many fish. Their light skeleton and oil-filled liver helps reduce its overall density, thus allowing it to ascend and descend in the water.
OBTAINING NUTRIENTS
Chondrichthyans teeth are embedded into the gums and not attached to the jaw. Depending on the species, the teeth can range from being very sharp and pointy for catching and eating fish, to flattened teeth for grinding food. Food and nutrients are absorbed in the intestines through spiral valves which increase the nutrient absorption. The food leaves the stomach and passes into the small intestine where the spiral valves are located. As the food passes through the spiral valve, the digestive tract leads it to the rectum and to the cloaca. Sharks have U shaped stomachs that use very strong acids and enzymes to dissolve most of what is eaten.
Chondrichthyans teeth are embedded into the gums and not attached to the jaw. Depending on the species, the teeth can range from being very sharp and pointy for catching and eating fish, to flattened teeth for grinding food. Food and nutrients are absorbed in the intestines through spiral valves which increase the nutrient absorption. The food leaves the stomach and passes into the small intestine where the spiral valves are located. As the food passes through the spiral valve, the digestive tract leads it to the rectum and to the cloaca. Sharks have U shaped stomachs that use very strong acids and enzymes to dissolve most of what is eaten.
RESPIRATION
Chondrichthyans respire through the use of gills. Most shark species have anywhere between 5-7 pairs of gill openings. Rays have 5 or 6 gill openings and chimaeras have 4 pairs of gill arches and only 1 pair of gill openings. The gill openings in sharks and chimaeras are located on the side behind the head, whereas the gill openings of rays and skates are located underneath the head. Rays and bottom dwelling sharks have spiracles, which are openings that allow water to be pumped over the gills while stationary, allowing them to rest on the seafloor. Other chondrichthyan groups need to continue to move through the water in order to breathe. Chimaeras however, have nostrils that take in the water instead of using their mouth.
Chondrichthyans respire through the use of gills. Most shark species have anywhere between 5-7 pairs of gill openings. Rays have 5 or 6 gill openings and chimaeras have 4 pairs of gill arches and only 1 pair of gill openings. The gill openings in sharks and chimaeras are located on the side behind the head, whereas the gill openings of rays and skates are located underneath the head. Rays and bottom dwelling sharks have spiracles, which are openings that allow water to be pumped over the gills while stationary, allowing them to rest on the seafloor. Other chondrichthyan groups need to continue to move through the water in order to breathe. Chimaeras however, have nostrils that take in the water instead of using their mouth.
CIRCULATION
Chondrichthyans have a closed circulatory system. They have a two chambered heart in which the blood enters the heart through the vein and exits through a vein on its way to the gills. In the gills, the blood picks up oxygen from the surrounding water and leaves the gills in arteries, which goes back to the body. The oxygen is used in the body and goes back to the heart. Chondrichthyes hearts are S-shaped tubes located in the head. Blood is pumped by the heart through the ventral aorta, to the capillaries in the gills, where blood is oxygenated. From the gills, the blood then flows through the paired dorsal aorta, then through the tissue of the body and then back to the heart in veins.
Chondrichthyans have a closed circulatory system. They have a two chambered heart in which the blood enters the heart through the vein and exits through a vein on its way to the gills. In the gills, the blood picks up oxygen from the surrounding water and leaves the gills in arteries, which goes back to the body. The oxygen is used in the body and goes back to the heart. Chondrichthyes hearts are S-shaped tubes located in the head. Blood is pumped by the heart through the ventral aorta, to the capillaries in the gills, where blood is oxygenated. From the gills, the blood then flows through the paired dorsal aorta, then through the tissue of the body and then back to the heart in veins.
EXCRETION
Waste is eliminated through the rectum and out of the cloaca, which is a small cavity at the end of the digestive tract. Some wastes diffuse through the gills and into the surrounding water. Their cloaca is shared by the genital organs and connects to the urinary and intestinal tracts. Nitrogenous waste is excreted as ammonia.
Waste is eliminated through the rectum and out of the cloaca, which is a small cavity at the end of the digestive tract. Some wastes diffuse through the gills and into the surrounding water. Their cloaca is shared by the genital organs and connects to the urinary and intestinal tracts. Nitrogenous waste is excreted as ammonia.
RESPONSE
Their nervous system consists of a small brain, a spinal column, and a network of nerves. Chondrichthyans have eyes with an excellent field of vision and some species are capable of seeing color. They have taste receptor cells that determine the taste of prey, by taste buds that cover a small bump in the mouth. Chondrichthyans have touch receptor cells located near the skin surface that respond to contact, the bending of the body, and fins, through the stretching and contraction of muscles. Sense of balance and body movement come from a series of organs inside the ear. They have an acute sense of smell and hearing. Chondrichthyans have electro-sensory organs, that are able to detect even the weakest electric fields generated by the movement of prey and predators.
Their nervous system consists of a small brain, a spinal column, and a network of nerves. Chondrichthyans have eyes with an excellent field of vision and some species are capable of seeing color. They have taste receptor cells that determine the taste of prey, by taste buds that cover a small bump in the mouth. Chondrichthyans have touch receptor cells located near the skin surface that respond to contact, the bending of the body, and fins, through the stretching and contraction of muscles. Sense of balance and body movement come from a series of organs inside the ear. They have an acute sense of smell and hearing. Chondrichthyans have electro-sensory organs, that are able to detect even the weakest electric fields generated by the movement of prey and predators.
REPRODUCTION
Chondrichthyans reproduce sexually and fertilization is internal. They usually give birth to live young but some species can develop young through eggs. There is no parental care after birth, but some chondrichthyans protect their eggs before they hatch. Chondrichthyes have separate sexes. Females have ovaries and urogenital tracts, where each is differentiated into an oviduct, oviducal gland and uterus, which open into a common urogenital sinus. Males have external paired calcified claspers, which are extensions of the pelvic fins and internal organs, that include the paired testes and genital ducts leading to the seminal vesicles.
Chondrichthyans reproduce sexually and fertilization is internal. They usually give birth to live young but some species can develop young through eggs. There is no parental care after birth, but some chondrichthyans protect their eggs before they hatch. Chondrichthyes have separate sexes. Females have ovaries and urogenital tracts, where each is differentiated into an oviduct, oviducal gland and uterus, which open into a common urogenital sinus. Males have external paired calcified claspers, which are extensions of the pelvic fins and internal organs, that include the paired testes and genital ducts leading to the seminal vesicles.