Ligament Used to Reopen Shells

close up photograph of black and yellow giant clam underwater

Biological Strategy

Mussels and clams

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Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

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Modify Position

Many resources that living systems require for survival and reproduction constantly change in quantity, quality, and location. The same is true of the threats that face living systems. As a result, living systems have strategies to maintain access to shifting resources and to avoid changing threats by adjusting their location or orientation. Some living systems modify their position by moving from one location to another. For those that can’t change location, such as trees, they modify position by shifting in place. An example of an organism that does both is the chameleon. This creature can move from place to place to find food or escape predators. But it also can stay in one place and rotate its eyes to provide a 360-degree view so that it can hunt without frightening its prey.

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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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A ligament in bivalve mollusks can reopen closed shells due to the presence of abductin, an elastic protein.

Image: Student of Marjan Eggermont at University of Calgary Schulich School of Engineering /

Image: derrekkeats /

“Another rubber is abductin found in the shell-opening ligaments of bivalve mollusks. One or two adductor muscles hold the two halfshells or valves of a bivalve closed (the edible part of a scallop is one of these muscles). Closing compresses the ligament, so its elastic resiliency can reopen the shell if the muscles relax. Interestingly, scallops, which swim by repeatedly clapping their valves together, recover a greater fraction of the work done on their abductin than do clams and other more sedentary forms.” (Vogel 2003:304)

Last Updated August 18, 2016

References

Book

Comparative Biomechanics: Life's Physical World, Second Edition

Princeton University Press | 17/06/2013 | Steven Vogel

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