Anus Absorbs Water

Biological Strategy

Woodlice

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Capture, Absorb, or Filter Liquids

The most common liquid used by living systems is water, which they require to survive. But there are many other liquids that provide nourishment, play a role in defense mechanisms, or serve other purposes. Water varies in its availability; it is sometimes plentiful and sometimes very scarce or only available as fog or mist. To minimize the energy required to capture, absorb, or filter liquids, living systems have strategies that take advantage of the unique properties of the given liquid. For example, water moves from a gaseous to liquid state when it encounters a surface colder than the air. Plants in forests that experience fog and clouds more than rain have strategies that condense liquid water from moist air.

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Crustaceans

Subphylum Crustacea (“crust”): Crabs, barnacles, shrimp, pillbugs

Some crustaceans, like pillpugs and woodlice, live on land, but most are found in the ocean. Their heads are distinctive among the arthropods: they have two pairs of antennae and three pairs of feeding appendages that help them hold and crunch food. Crustaceans also have a unique larval stage called the nauplius (named after the son of Poseidon) which has three pairs of legs and one eye. Most crustaceans are in class Malacostraca, which contains a wide range of species that live in mostly marine environments, like krill, lobster, and mantis shrimp.

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The anus of some woodlice can soak up water using posterior abdominal appendages and capillary action.

Roly Polies Came From the Sea to Conquer the Earth

“1. Experiments were undertaken to determine the site of water uptake, and the conditions in which it occurs, in Ligia oceanica, Oniscus asellus, Porcellio scaber and Armadillidium vulgare.

“2. Besides absorbing water with moist food, all four species were capable of active imbibition of water through both mouth and anus when a free water surface was available. In Ligia oceanica, imbibition occurred largely through the anus, in other species, through the mouth.” (Spencer 1954:496)

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