The shells of the rough fileclam aid movement through water via jet propulsion.
“When danger threatens, this scallop claps its shells together and darts through the water, like a pair of castanets with a life of their own.” (Downer 2002:14)
Image: Damsea / Shutterstock / Some rights reserved
Move in/on Liquids
Water is not only the most abundant liquid on earth, but it’s vital to life–so it’s no surprise that the majority of life has evolved to thrive on and under its surface. Moving efficiently in and on this dense and dynamic substance presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag, utilize surface tension, fine tune buoyancy, and take advantage of various types of currents and fluid dynamics. For example, sharks can slide through water by reducing drag due to their streamlined shape and specially shaped features on their skin.
Expel Liquids
There are various reasons living systems discharge liquids, such as to defend themselves, to avoid liquid buildup that can cause decay, to eliminate waste, or to dry off. Because liquids cannot be effectively moved through pushing, a different kind of force is needed to expel them. Creating that force requires energy, so living systems must have efficient strategies worth the energy investment or use an outside force (such as gravity). This typically entails strategies that build up pressure or use other forces to propel liquids away. An example of a living system that expels liquids is the scallop. This creature moves through water by clapping its shells together, generating a water jet that propels it in the opposite direction.
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.
