All animals
are motile, meaning they can move spontaneously and independently, at
some point in their lives. All animals are heterotrophs: they must
ingest other organisms or their products for sustenance.
Most known
animal phyla appeared in the fossil record as marine species during
the Cambrian explosion, about 542 million years ago. Animals are divided
into various sub-groups, some of which
are: vertebrates (birds,mammals, amphibians, reptiles, fish); molluscs (clams, oysters, octopuses,squid, snails); arthropods (millipedes, centipedes, insects, spiders, scorpions,crabs, lobsters, shrimp); annelids (earthworms, leeches); sponges;
and jellyfish.
Contact with animals resulted in roughly 80,000 human
deaths in 2013, down from 96,000 in 1990.More than 70% of these deaths
were from venomous animals.
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