Eyes Detect Changing Movement Patterns

a queen scallop shell is slightly opened, with red algae growing around it, on the top and bottom edge of the shell there are many small blue and black eyes

Biological Strategy

Queen scallop

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Image: Natural England/Ross Bullimore / Flickr / CC BY - Creative Commons Attribution alone

Sense Light (Visible Spectrum) From the Environment

Living systems constantly receive signals from their environment that help them survive. Light (in the visible spectrum) can come from other living systems (such as fireflies) or from non-living sources (such as the sun). Survival often depends on sensing and responding to challenges like low light conditions or light that has been altered in some way. Because basic survival is at stake, living systems must excel at meeting those challenges. A well-known phenomenon is how water bends light. A stork trying to catch a fish underwater can compensate for this bending effect so that when it strikes at the fish, it has a good chance of catching it.

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Sense Motion

Perceiving motion is important for a living system to sense where it is in relation to a moving environment, which is critical in locating resources or wayfinding. This applies whether the environment itself is in motion (such as water movement coming from a nearby fish) or the living system is moving within a stationary environment (such as a bird flying through the air). Because motion dampens over distance and the cost of missing those motion signals is high, living systems must be quite sensitive to these signals. For example, fast-flying big brown bats have microscopic, stiff, domed hairs on their wing membranes that act as a sensor array to monitor flight speed and airflow conditions.

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Bivalves

Class Bivalvia (“two-valved”): Clams, mussels, oysters

The bivalve name says it all: these animals are characterized by a two-sided shell that is connected at the hinge with a muscle. The 15,000 species in 90 families have flattened bodies, no head, and generally live a sedentary lifestyle. Instead of having a circular band of teeth like other molluscs, many are filter feeders. They use cilia, or hair-like extensions, to move water into their bodies and pluck out plankton to eat. Consequently, there are no terrestrial bivalves, and only 15% live in freshwater ecosystems. The rest live in marine environments.

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The numerous simple eyes of the queen scallop detect changing patterns of movement using two retinas, one that responds to light and the other to darkness.

Image: Jan Johan ter Poorten; modified by Tom Meijer / Wikimedia Commons /

''Aequipecten opercularis''; marine bivalved shell commonly occurring in the North Sea.

Image: Lycaon (talk) / Wikimedia Commons /

Digital StillCamera

Image: Jan Johan ter Poorten / Wikimedia Commons /

Eyes of queen scallop, lined up like a string of jewels, detect light and movement.

“The scallop is the record holder for sheer numbers of eyes. It may have from 50 to 200 simple eyes, strung along the edge of its mantle like a string of glistening beads.

“The eyes of a queen scallop are dotted all around the edge of its mantle. The jewel-like effect is due to a reflecting layer or tapetum behind each eye. Scallop eyes contain two types of retina — one responds to light, the other to sudden darkness, such as the shadow cast by an approaching predator. The scallop probably cannot interpret shapes, but can detect changing patterns of movement, such as moving light-dark changes.” (Foy and Oxford Scientific Films 1982:118)

Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.

Last Updated August 18, 2016

References

Book

The grand design: Form and colour in animals

BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London | 26/02/1983 | Sally Foy

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