Animals that manufacture their own homes

Many species of mollusc have hard external coverings, commonly known as "sea shells", even though there are also a number of fresh-water mollusc species with shells and snails with shells that live on dry land. Turtles and tortoises also have shells. In general, because the animal is attached to its shell, it has become less mobile. However, the shell provides protection and also serves as an external skeleton for these animals. Of course, some predators have developed techniques for separating the shell-dweller from its shell.

Although many of these creatures have been particularly successful to date, having survived over millions of years, shelled animals have also been adversely affected by human activities:

  • loss of breeding habitat. Turtles are also frequently killed when crossing roads.
  • fresh-water molluscs are affected by declining water quality
  • over-consumption of edible molluscs
  • pollution threatens species that live in fresh water
nautilus
Image Courtesy: National Science Foundation
The shell protects these animals against most predators, but it cannot defend them against the deterioration of their habitat.

Corals also manufacture an external shell-like structure that provides them with protection and an external skeleton.

Shell links

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