Deployable Web Distracts Predators

a mulitcolored iridescent octopus swims lengthwise across the photo against a black background

Biological Strategy

Common blanket octopus

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Modify Size/Shape/Mass/Volume

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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Cephalopods

Class Cephalopoda (“head-foot”): Nautilus, squid, octopus, cuttlefish

Cephalopods are unique among mollusks, and even within the animal kingdom. They are lauded for their large brains and complex behaviors and are considered the most intelligent invertebrates. Among 800 species in 45 families, all are carnivorous and live in marine ecosystems. They all have a set of arms or tentacles, but only the nautilus retains an exterior chambered shell. Many species have chromatophores, which allow them to change color for defense, camouflage, or courting. They range from the size of a fingernail to just longer than a city bus (the mysterious giant squid).

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The membrane attached to some arms of the blanket octopus serves as a defense mechanism because it expands to distract predators and can be shed if necessary.

“The appearance of the female is striking due to the wide, deep web attached to arms I and II (Portmann 1952), for which the name ‘blanket’ or ‘handkerchief’ octopus has been given (Voss and Williamson 1971). The web is most extensive between arms I and II and it can be expanded or contracted to a remarkable degree. Contractions of the web are due to transverse bands of muscle, each surrounded by elastic fibres which probably allow the web to expand after autotomy. Besides this the edge of the web, parallel with the arm, has a row of ‘pouches’ lined by glands; these may have a role in the attachment of the clusters of stalked eggs (Portmann 1952). Autotomy of the web occurs along visible fracture lines when the animal is distressed. The dorsal arms and web are held rolled back when the animal swims, but spread out if disturbed. The web undoubtedly has several functions, as it does in Argonauta…The web when fully extended was 600mm long and 300mm wide, and the animal had a mantle length of 180 mm.” (Nixon and Young 2003:324)

Last Updated August 18, 2016

References

Book

The Brains and Lives of Cephalopods

Oxford University Press | Nixon, Marian; Young, John Zachary

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