Joint Aids Suspension Feeding

Biological Strategy

Gurney's sea pen

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Capture, Absorb, or Filter Organisms

Many living systems must secure organisms for food. But just as one living system must capture its prey to survive, its prey must escape to survive. This results in capture and avoidance strategies that include trickery, speed, poisons, constructed traps, and more. For example, a carnivorous plant called the pitcher plant has leaves formed into a tube that collect water. Long, slippery hairs within the tube face downward. When insects enter the tube seeking nectar, they lose their footing and slide inside, unable to climb out and escape being eaten and digested by the plant.

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Manage Turbulence

A turbulent force occurs when air or water creates a chaotic or irregular motion. The source can be such things as wind, waves, and eddies caused by obstructions to air or water flow (such as that created by a rock in a stream). Because the force is irregular, it acts in unpredictable ways on multiple parts of a living system at any given time, decreasing the living system’s efficiency. Strategies used to manage turbulence include dampening the amount of turbulence, having flexibility to handle sudden changes, and making quick adjustments. An example is the mucus on aquatic organisms, such as barracuda sharks, that can reduce turbulent friction of seawater by 66%. In doing so, it decreases drag and increases the sharks’ swimming efficiency.

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Jellyfish

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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A joint in sea pens enhances suspension feeding by allowing them to twist to face the current.

“Twisting about a lengthwise axis only. This kind of joint, rare in nature, turns up in sea pens (Ptilosarcus), which stand unbent on bay bottoms and rotate so they face the current (Best 1988). The ascidian, Styela…does much the same thing (Young and Braithwaite 1980)–and for the same reason, taking advantage of ambient currents for suspension feeding. Pushing up the twistiness-to-bendiness ratio of a cylinder, of course, restricts bending relative to twisting and thus encourages just this kind of specific torsional flexibility, but without an absolute prohibition on hinge action and without a discrete joint.” (Vogel 2003:403)

Vogel S. Comparative Biomechanics: Life’s Physical World. Princeton: Princeton University Press; 2003. 580 p.

Last Updated August 18, 2016

References

Book

Comparative Biomechanics: Life's Physical World, Second Edition

17/06/2013 | Steven Vogel

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