Stalk Structure Improves Feeding Position

the tall orange stalk of a plumose anemone holds a top of thin white tentacles

Biological Strategy

Clonal plumose anemone

AskNature Team

Image: Emőke Dénes / Wikimedia Commons / CC BY - Creative Commons Attribution alone

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.

Search this Function

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.

Search this Function

Coral and sea anemones

Class Anthozoa (“flower animals”): Corals and sea anemones

Most cnidarians are included in this class, which contains 6,000 species and 70% of all known cnidarians. These animals are exclusively found in marine environments. They have no jellyfish-like medusa stage, and so move very little or not at all throughout most of their life. They are carnivores and channel food down a groove lined with cilia, or hair-like appendages, to their mouths. Many also have a symbiotic relationship with photosynthetic algae, which are responsible for the vibrant colors associated with coral colonies.

Search this Living System

The stalk of a tall sea anemone maximizes the anemone's feeding postion by bending at its narrowest part, just below its crown of tentacles.

Clonal plumose anemone, various degrees of bending.

Image: Wikimedia Commons /

Image: Thesupermat / Wikimedia Commons /

“In some cases, nature capitalizes on the way hollow tubes bend. A tall sea anemone, Metridium, has an area of its columnar body just beneath the crown of tentacles that is narrower than anywhere else, as in figure 18.9. The material properties of the stalk don’t vary, but when a gentle water current is present, the stalk bends at this point rather than at the bottom, and the tentacles are exposed broadside to the flow in the best position for feeding on suspended matter (Koehl 1977b). It doesn’t take much narrowing to concentrate the bending–I [the second moment of area], as equation (18.1) shows, depends strongly on radius.” (Vogel 2003:376)

Last Updated August 18, 2016

References

Book

Comparative Biomechanics: Life's Physical World, Second Edition

17/06/2013 | Steven Vogel

embedly preview

Reference

Journal article

AskNature