When a living system is under compression, there is a force pushing on it, like a chair with a person sitting on it. When evenly applied to all sides of a living system, compression results in decreased volume. When applied on two sides, it results in deformation, such as when pushing on two sides of a balloon. This deformation can be temporary or permanent. Because living systems must retain their most efficient form, they must ensure that any deformation is temporary. Managing compression also provides an opportunity to lessen the effects of other forces. Living systems have strategies to help prevent compression or recover from it, while maintaining function. For example, African elephant adults weigh from 4,700 to 6,048 kilograms. Because they must hold all of that weight on their four feet, the tissues of their feet have features that enable compression to absorb and distribute forces.
Subphylum Medusozoa (“serpent-haired monster animals”): Jellyfish, box jellyfish, hydrozoans
Medusozoans spend at least part of their life cycle in the medusa stage, where they form a bell-like shape with tentacles, allowing them to move freely. Within this subphylum, Class Scyphozoa (“cup animals”) include true jellyfish that have a thick, gelatinous body and live their adult lives as medusa. There are a few hundred species of scyphozoans. Class Cubozoa, often called “box jellyfish” get their name from their cube-shaped bodies, may be incredibly venomous, and have complex eyes, which are unusual among cnidarians.
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