D. KNOPand his colleagues published a study demonstrating that
some planktonic-living dinoflagellates have an ocelloid
similar to the eye, consisting of individual components
comparable to the cornea, iris, lens, and retina. As com-
prehensive investigations have shown, this ocelloid is
built up from cell components of several different for-
mer endosymbionts.
The anatomical complexity of a single cell is very lim-
ited, because there are not that many components that
could further differentiate. Therefore, a single cell can-
not develop a complex lens eye from its own cell com-
ponents. However, the example of the dinoflagellates
shows that a single cell can also use cell components
from other organisms, combining them to create an eye-
like structure. After all, this ocelloid with lens and iris
is so complex that scientists initially thought it was a
multicellular eye.
In the end, we can only marvel at the variety of eyes
that are found in the sea and in our aquariums. “An ani-
mal’s eyes have the power to speak a great language,” as
the Israeli philosopher Martin Buber once wrote, and
having an appreciation for the visual perspectives of the
animals we keep is not only fascinating but something
every aquarist can use in day-to-day reef husbandry. It
can help us to provide appropriate food, security, light
levels, and stress-free surroundings.REFERENCES
Gavelis, G.S., S. Hayakawa, R.A. White III, and B.S. Leander. 2015.
Eye-like ocelloids are built from different endosymbiotically
acquired components. Nature 523: 204–7, doi: 10.1038/
nature14593.
Land, M.F. 1984. Molluscs, in Photoreception and Vision in
Invertebrates, NATO ASI Series, vol. 74, pp. 699–725.
Janouskovec, J., A. Horak, M. Obornik, and P.J. Keeling. 2010. A
common red algal origin of the apicomplexan, dinoflagellate,
and heterokont plastids. Proc Nat Acad Sci USA 107: 10949–54.
Parker, A. 2003. In the Blink of an Eye: How Vision Sparked the Big
Bang of Evolution. Basic Books, New York.
Storch, V. and U. Welsch. 2005. Kurzes Lehrbuch der Zoologie, 8th
edition. Spektrum Akademischer Verlag, Heidelberg.
Thoen, H., M.J. How, T.-H. Chiou, and J. Marshall. 2014. A
different form of color vision in mantis shrimp. Science 343,
6169: 411–13, doi: 10.1126/science.1245824.ON THE INTERNET
Gehring, W.J. 2012. Auge um Auge—Entwicklung und
Evolution des Auges. http://bit.ly/Jli6Zy.
UC Berkeley, A Fish Eye View of Life. http://evolution.berkeley.
edu/evolibrary/article/fishtree_01.The human eye (shown) adjusts to changing light
intensity by expanding or narrowing the iris. The
iris of the fish eye is not capable of this. Fishes
compensate for differences in brightness in a
completely different way.
The tapetum lucidum of this
Cryptocentrus goby’s eye can
be seen in the background.
The spherical lens is also
clearly visible.The eyes of fishes adjust to varying amounts of light by
retracting the photosensitive rod receptors into the protective
pigment cell layer, while the less light-sensitive cone receptors
remain exposed. Very few fishes can narrow the pupils.