All chordates have a number of structures in common:
The main taxa within Phylum Chordata include:
|Class Agnatha (a- = not, without; gnatho = jaw) which is the lampreys. They do not have jaws, are eel-shaped, prey on fish, and have larval forms which are different from the adults.|
|Class Chondrichthyes (chondro = cartilage; ichthys = fish) which includes sharks and rays. They have a cartilage skeleton, not bone. They are not buoyant like other fish so they must swim or sink. Like other fish they have a lateral line system which detects differences in water pressure, the equivalent of our hearing.
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|Class Osteichthyes (osteo = bone) is the bony fish. This is the most numerous of all vertebrate classes. In fish, O2 is exchanged via the gills, which are covered by an operculum which helps to draw water across/through the gills. Their swim bladder is an air sac used to control buoyancy, thus unlike the sharks, bony fish can hold still at any depth and not sink.|
|Class Amphibia (amphi = on both sides, double; bios = life) is frogs, newts, and salamanders. They were the first land vertebrates. Frogs, especially, go through metamorphosis. Their eggs have no egg shells, so the sperm can swim through the water to the eggs, and the embryos must develop in water.|
|Class Reptilia (reptili = creeping) is the dinosaurs (dino = terrible ), snakes, turtles, crocodiles, and lizards. Reptiles have scales and are dry to the touch. Their eggs have leathery shells. Reptiles are exothermic (exo = out, outside), that is they maintain their body temperature through external means such as sunning on a rock or seeking shade. Reptiles need less food/energy to live and live longer than a comparable-sized mammal. Some dinosaurs may have been endothermic.|
|Class Aves (avi = a bird) is the birds. It is thought that birds are descended from dinosaurs, as evidenced, in part, by the scales on their feet. Also, feathers are modified scales: a key characteristic of birds is that they have feathers. Birds’ bones are light weight for flight. Birds are endothermic (endo = within, inner), that is, they control their body temperature from within (they’re “warm-blooded”). Birds’ vision is the best of all vertebrates: soaring hawks can spot small mice scrambling through the grass in a field far below them. Birds have shelled eggs and so must have internal fertilization — the egg muct be fertilized before the hen’s reproductive tract secretes an eggshell. Generally, mating is accompanied by an elaborate courtship ritual. Eggs and often young birds are more exothermic (are not able to control their body temperatures from within) and so must be brooded/incubated by parents.|
|Class Mammalia (mamma, mammil = teat, nipple) is the mammals. Key characteristics of mammals are the presence of fur/hair and mammary glands, derived from modified sweat glands, which produce milk for the young. Mammals have a diaphragm to aid in respiration. They are endothermic. Most mammals bear live young.|
|Order Artiodactyla includes sheep, pigs, cattle, deer, giraffes, and goats which have even-toed hooves and are herbivorous.|
|Order Carnivora (carni = flesh; vore = eat, devour) includes cats, dogs, bears, seals, walruses, skunks, and racoons. These are carnivorous and have pointed canine teeth and molars.|
|Order Cetacea (ceta = a whale) includes whales, dolphins, and porpoises which are aquatic/marine. Their front legs (equivalent to our arms) are fin-like, and they have no hind legs. They have a thick layer of blubber for insulation.|
|Order Chiroptera (chiro = a hand, like chiropractor; ptera = wing, feather) is the bats. Their fingers are webbed to create wings.|
|Order Edentata includes sloths, anteaters, and armadillos. They have reduced or no teeth.|
|Order Insectivora (vora = to eat, devour) includes moles, shrews, and hedgehogs which eat insects.|
|Order Lagomorpha includes the rabbits, which have chisel-like incisors and hind legs modified for jumping.|
|Order Perissodactyla includes horses, tapirs, and rhinoceros which have odd-toed hooves and are herbivorous.|
|Order Primates (prima = first) includes lemurs, monkeys, apes, and humans. These have opposable thumbs and eyes that face forward.|
|Order Proboscidae includes elephants which have long, muscular trunks and thick, loose skin. Their upper incisors are elongated as tusks.|
|Order Rodentia (roden = gnaw, gnawing) includes squirrels, beavers, rats, porcupines, woodchucks, guinea pigs, and mice. These have chisel-like, constantly-growing incisors.|
|Order Sirenia includes manatees which are aquatic herbivores. Their front legs (“arms”) are fin-like, and they have no hind legs.|
Note that humans (mammals) are to reptiles as insects are to centipedes, and humans (mammals) are to Amphioxus as insects are to spiders.
Copyright © 1997 by J. Stein Carter. All rights reserved.
Clipart edited from Corel Presentations 8
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