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The mammals
comprise a large group of warm-blooded vertebrate animals characterized
by having mammary glands in the female; these are used for suckling the
young. Other features of mammals are hair (very reduced in some species,
such as whales); a middle ear formed of three small bones (ossicles); a
lower jaw consisting of two bones only; seven vertebrae in the neck; and
no nucleus in the red blood cells. |
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There are over
4,000 species of mammals, adapted to almost every way of life. The
smallest shrew weighs only 2 g/0.07 oz, the largest whale up to 140
metric tons/154 US tons. As with every other animal group, a number of
mammal species are in danger of extinction from habitat loss and
hunting. According to the Red List of endangered species published by
the World Conservation Union (IUCN) for 1996, 25% of mammal species are
threatened with extinction. |
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Mammals are
divided into three groups: placental mammals (the largest group),
such as humans, wolves, armadillos, bats, and shrews; marsupials,
such as kangaroos, koalas, and wombats; and monotremes, such as
platypuses and echidnas (spiny anteaters). |
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Most mammals are
placental mammals, where the young develop inside the mother's body, in
the uterus, receiving nourishment from the blood of the mother via the
placenta. There is considerable variation among |
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Major
Invertebrate and Vertebrate Groups |
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Invertebrates |
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Taxon1 |
Name |
Examples |
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P |
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Porifera |
all sponges |
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P |
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Cnidaria |
corals, sea
anemones, Hydra, jellyfishes |
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P |
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Ctenophora |
sea
gooseberries, comb jellies |
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P |
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Platyhelminthes |
flatworms,
flukes, tapeworms |
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P |
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Nemertina |
nemertine worms,
ribbon worms |
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P |
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Nematoda |
roundworms |
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P |
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Mollusca |
clams, oysters,
snails, slugs, octopuses, squids, cuttlefish |
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P |
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Annelida |
ringed worms,
including lugworms, earthworms, and leeches |
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P |
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Arthropoda |
(subdivided into
classes below) |
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C |
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Arachnida |
spiders, ticks,
scorpions, mites |
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C |
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Branchiopoda |
water fleas |
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C |
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Cirripedia |
barnacles |
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C |
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Malacostraca |
crabs, lobsters,
shrimp, woodlice |
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C |
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Diplopoda |
millipedes |
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C |
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Chilopoda |
centipedes |
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C |
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Insecta |
silverfish,
dragonflies, mayflies, stoneflies, cockroaches, earwigs, web
spinners, termites, booklice, lice, grasshoppers, thrips,
lace-wings, scorpion flies, caddis-flies, moths, butterflies,
beetles, house flies, fleas, stylopids, ants, bees |
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P |
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Echinodermata |
sea stars,
brittle stars, sea urchins, sand dollars, sea cucumbers |
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P |
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Hemichordata |
acorn worms,
pterobranchs, graptolites |
Vertebrates |
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Taxon1 |
Name |
Examples |
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C |
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Agnatha |
(jawless fishes)
lampreys, hagfishes |
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C |
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Chondricthyes |
(cartilaginous
fishes) dogfish, sharks, rays, skates |
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C |
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Osteichthyes |
(bony fishes)
salmon, catfishes, perches, flatfishes including flounder and
halibut |
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C |
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Amphibia |
frogs, toads,
newts, salamanders, caecilians |
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C |
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Reptilia |
tuatara,
tortoises, turtles, lizards, snakes |
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C |
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Aves |
rheas,
ostriches, moa, penguins, ducks, pheasants, gulls, swifts,
kingfishers, sparrows, woodpeckers, pelicans, flamingoes, herons,
falcons, cranes, divers, pigeons, parrots, cuckoos, owls |
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C |
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Mammalia |
duck-billed
platypuses, echidnas, kangaroos, opossums, shrews, bats, dogs,
seals, whales, dolphins, rats, rabbits, pigs, camels, deer, horses,
tapirs, elephants, hyraxes, anteaters, manatees, pangolins, lemurs,
monkeys, humans |
1 P
represents phylum; C represents class. |
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