Body Changes Stiffness

a dark hole opens in beige skin of a cucumber with brown and red bumps and spots

Biological Strategy

Leopard sea cucumber

AskNature Team

Image: Klaus Stiefel / Flickr / Some rights reserved

Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

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Gastropods

Class Gastropoda (“stomach-foot”): Snails and slugs

There are at least 40,000 known species of gastropod, with many more yet to be discovered, making it the largest class of mollusks. These animals exhibit torsion, meaning their internal organs are twisted 180° during development. The majority of gastropods have shells, and most open up on the right side. The largest gastropods are the size of a small child (3 feet, or 1 meter) while the smallest are barely visible to the naked eye.

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The body of the sea cucumber changes from soft to standard to hard due to stiffening and plastizing factors and exuding water.

“Catch connective tissues or mutable collagenous tissues of echinoderms can extensively change their mechanical properties such as elasticity and viscosity within a few minutes under the regulation of their nervous system. The tissues contain a large amount of the extracellular matrix, mainly consisting of collagen fibrils, proteoglycans and microfibrils. The unique properties of these collagenous tissues might be due to lack of permanent associations between the collagen fibrils and the surrounding extracellular matrix because it is easy to isolate collagen fibrils from catch connective tissues – unlike collagenous tissues of adult vertebrates. It seems that crosslinking of the collagen fibrils with adjacent ones and other components of the extracellular matrix is formed or broken during changes in the mechanical properties of catch connective tissues. The molecular mechanisms underlying the change are, however, not yet fully understood. The holothurian body wall dermis is a typical catch connective tissue that shows rapid and reversible changes in its mechanical properties in response to various stimuli. Extensive studies on the dynamic mechanical properties of the dermis of the sea cucumber Actinopyga mauritiana revealed that the tissue can adopt at least three different states. These are stiff, standard and soft states, which can be distinguished by elastic and viscous properties and by strain-dependent behaviors…The mechanical parameters of the standard state are not simply the intermediate values between the stiff and the soft states, suggesting that the molecular mechanism converting the soft to the standard state is different from that converting the standard to the stiff state.” (Yamada et al. 2010:3416)