Researchers solve mystery after examining 25 years of video footage
The animals in the deep seas comprise some of the most mysterious
inhabitants of our oceans.
Case in point: a squid with eyes that are of
different sizes, aptly named the cockeyed squid (Histioteuthis
Also known as the strawberry squid, one of its eyes is large and
yellow, while the other eye is small and bluish. A related species,
Stigmatoteuthis dofleini, has a protruding eye on one side and a normal
eye on the other side.
Although these species were discovered more than a century ago,
biologists have long been puzzled over the reason of the asymmetrical
qualities of the two eyes. Now, after analysing 25 years' worth of
video footage of the squids taken at depths of 200 to 1,000 metres,
researchers have discovered the answer.
Their findings have been
recently published in the journal Philosophical Transactions of the
Royal Society B.
It seemed that the larger eye was always being directed upwards, while
the smaller eye was directed downwards, indicating that the eyes served
The larger eye, with its yellow lens, allowed the
squid to detect prey against the dim down welling surface light, and
makes them easier to spot.
The smaller eye specialised in scanning for
bright bioluminescent fashes emitted by prey in the dark waters from
As such, the smaller size of the downward-directed eyes enables less
energy usage, thereby maximising the squid's “energy efficiency”.
Link to the study