Four-eyed spookfish has mirror eyes
Posted on homepage: 1 November 2010 (GMT+10)
The brownsnout spookfish (Dolichopteryx longipes)1, a strange denizen of the deep, has been known for 120 years, but its amazing optics have only recently been worked out.
Even in clear water, sunlight is quickly absorbed with depth,2 so there is hardly any light at 1,000 m (3,000 ft). So creatures need special features to see in such minimal light. Many of them, including the spookfish, have tubular eyes that point upwards towards the surface. This is “like having a telescope on your head that points towards the surface”, according to Ron Douglas of the City University of London.
However, if that’s all they had, they would miss out on a lot. Many creatures at that depth emit their own light, bioluminescence, produced very efficiently by chemical energy, with hardly any heat.3 But the spookfish has this covered. A recent catch by Professor Hans-Joachim Wagner from Germany’s Tübingen University, between New Zealand and Samoa,4 startled researchers because it seemed to have four eyes, although “vertebrates with four eyes don’t exist,” says Dr Douglas.5
But closer examination found that they really have only two eyes, but each of them has two parts.6 It’s not the only fish like that. The strange fish Anableps anableps also has two parts to each eye, so is called a “four-eyed fish”. But Anableps lives near the water surface, and its unique “bifocal” eye produces two images, one from above the surface and one from below.7
With this deep-sea spookfish, the tubular part looks up, as expected, but the other part looks down. But instead of a lens, this one uses a mirror to focus light, i.e., by reflection rather than refraction. Professor Julian Partridge from the University of Bristol discovered that the mirror uses tiny plates of silvery crystals, probably of the DNA base guanine, stacked into multiple layers. Silvery fish are silvery because they have such crystals. But the crystals in this spookfish eye are not parallel to the surface of the mirror. Instead, they are precisely oriented, with the angle changing around the mirror. Prof. Partridge’s computer modelling shows that this arrangement produces a well-focused image.
This is not the only creature to have a reflective eye. The lobster has an exquisite reflective compound eye with square facets and a precise geometric arrangement that has inspired the design of X-ray telescopes.8 But the brownsnout spookfish is the only vertebrate so far discovered to have a focused reflective eye.
Naturally, there was the obligatory vacuous homage to evolution. Prof. Partridge said: “In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes—how to make an image—using a mirror.”4
But this bald assertion fails to show how random mutation and natural selection formed an accurate reflecting eye. Rather, it’s logical to believe that a solved problem points to a problem Solver (cf. John 9:32).
References and notes
- Several different varieties of fish have been independently named “spookfish”. Return to text.
- This is the normal exponential attenuation as radiation is absorbed by matter, as per the Beer–Lambert Law: I = I010 -αl where I0 and I are incident and transmitted light intensity, α is absorption coefficient and l = distance the light travels through the material (path length). Return to text.
- See Sarfati, J., Octopus suckers: glowing in the dark, Creation 21(3):6, 1999; <creation.com/octopus>. Return to text.
- Spookfish uses mirrors for eyes, Science Daily, 8 January 2009; <www.sciencedaily.com/releases/2009/01/090107134539.htm>. Return to text.
- Griggs, J., You can’t hide from a four-eyed spookfish, New Scientist 201(2689):11, 3 January 2009. Return to text.
- Wagner, H., and 4 others, A novel vertebrate eye using both refractive and reflective optics, Current Biology 19(2):108–114, 27 January 2009. Return to text.
- Grigg, R., The fish with “four eyes” (Anableps), Creation 18(1):52, 1995; <creation.com/anableps>. Return to text.
- Sarfati, J., Lobster eyes—brilliant geometric design: Lobster eyes, X-ray telescopes, and microchips, Creation 23(3):12–13, 2001; <creation.com/lobster>. Return to text.