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(Читай, слухай і вивчай!)
The animals have been divided into two groups based on the presence or absence of a backbone. The backbone is the observable feature that defines whether the animal is a vertebrate or an invertebrate.
backbone — [ˈbæk.bəʊn] — хребет, кістяк
vertebrate — [ˈvɜː.tɪ.brət] — хребетний
invertebrate — [ɪnˈvɜː.tɪ.brət] — безхребетний
- These groups are divided into smaller 'sub-groups'.
Sponges, corals, worms, insects, spiders and crabs etc. are all sub-groups of the invertebrate group – they do not have a backbone.
Fish, reptiles, birds, amphibians and mammals are different sub-groups of vertebrates – they all have internal skeletons and backbones.
Джерела:
https://www.oum.ox.ac.uk/thezone/animals/animalid/divide.htm