Fish breathe through the ____, while other vertebrates usually breathe through the ____. Their bodies are covered with ____ and their swimming limbs are called ____. ____ fish have a swim bladder. Fish eggs do not have ____. However, in the rest of the ____ vertebrates, in order to avoid ____, there are eggs with shells. Mammalian mouths have lips for ____ milk. Breasts have ____, except in monotremes. In monotremes the young have to ____ the milk. In marsupials there is no placenta, so the young must remain inside the marsupial ____ after leaving the ____.

Vertebrates.

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