Flexible Cylinders Siphon Water

Biological Strategy

Mussels and clams

AskNature Team

Image: pfly /

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Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Bivalves

Class Bivalvia (“two-valved”): Clams, mussels, oysters

The bivalve name says it all: these animals are characterized by a two-sided shell that is connected at the hinge with a muscle. The 15,000 species in 90 families have flattened bodies, no head, and generally live a sedentary lifestyle. Instead of having a circular band of teeth like other molluscs, many are filter feeders. They use cilia, or hair-like extensions, to move water into their bodies and pluck out plankton to eat. Consequently, there are no terrestrial bivalves, and only 15% live in freshwater ecosystems. The rest live in marine environments.

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Siphons used by clams to inhale and exhale water are effective due to their flexibility and extensibility.

“Cylinders may also act as pipelines carrying one material through another, like underground pipes. Man’s oil or drainage pipelines are usually rigid, but in nature flexibility is more valuable for this purpose. Some bivalve molluscs, such as clams, can live quite deep under the sandy sea bed by virtue of their extensible cylindrical siphons, one for inhaling water and the other for exhaling it after the gills have extracted food and oxygen.” (Foy and Oxford Scientific Films 1982:23)

Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.