Animal
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Animals are multicellular, eukaryotic organisms belonging to the biological kingdom Animalia. Animals consume organic material, breathe oxygen, have muscle cells, can reproduce sexually, and grow from
Sexual reproduction is nearly universal in animals, such as these dragonflies.
Predators, such as this ultramarine flycatcher (Ficedula superciliaris), feed on other animals.
Hydrothermal vent mussels and shrimps
The blue whale is the largest animal that has ever lived; it can be up to 33.6 metres (110 ft) long.
Bilateria
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Bilateria is a large clade of animals characterised by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front and a rear end, as
Animal
…of animal behaviour is known as ethology. The animal kingdom is divided into five major clades, namely Porifera, Ctenophora, Placozoa, Cnidaria and Bilateria. Most living animal species belong to the clade Bilateria, a highly proliferative clade whose members have a bilaterally symmetric and significantly…
EB1911 Crustacea Fig. 12.—Nauplius of a Prawn
One view is that the original bilaterian was a marine worm somewhat like Xenoturbella.
Ikaria wariootia, living 571–539 million years ago, is one of the oldest bilaterians identified.