Why don’t slugs have shells?

Snails are shell-fishly hoarding all the shells. 

4th September 2017
Why don’t slugs have shells? (Getty)

Asked by: Sally Thompson, Burnley

Slugs belong to a group of animals called molluscs. While slugs have no apparent shell, some species may have a reduced shell, or one that is internal, and therefore not visible. It is believed that the first mollusc-like animals were shell-less, with reduced or internal shells emerging later, and external shells evolving after that. This may seem strange, as molluscs have soft bodies, making them easy, vulnerable prey. But while shells do give some protection, they can also slow you down, so molluscs have extremely diverse survival strategies, which include camouflage, colouration, detaching their back appendages (as some lizards do) and chemical defences. 

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