Box jellyfish eyes surprise scientists
Scientists have known for over a century that box jellyfish (also known as cubozoans, after their cubic shape) have a unique array of eyes. They have 24 in total, of four different types.
Eight eyes resemble those of vertebrates (i.e. creatures with a backbone, e.g. humans),1 featuring “a sophisticated lens, retina, iris and cornea, all in an eye only 0.1 millimetres across”.2 But the specifics of function and performance hadn’t been explored—it was known only that its eyes gave the box jellyfish sufficient vision to respond to light and shadows, and to steer away from obstacles. (Box jellyfish do not just ‘drift’ along and eat whatever their tentacles ensnare; rather they are active predators, swimming towards objects of interest and avoiding others.)
Thus box jellyfish presented something of a riddle to evolutionists who acknowledged, “it has been a puzzle why they need such a complex set of eyes”,3 i.e. if the jellyfish only needed to discern light from dark. At the same time, their evolutionary paradigm held that “jellyfish belong to one of the first groups of animals to evolve eyes (the phylum Cnidaria)” and therefore “understanding how their eyes operate will show scientists what eyes were like early in evolutionary time.”1
So researchers investigated further. They noted from close-up video recordings of the box jellyfish species Tripedalia cystophora, that its four upper lens eyes and the pit eyes always point straight upward,4 irrespective of the direction of swimming or the orientation of the bell—even when the animal was completely upside down.
From further tests with jellyfish in tanks and underwater optical simulations, the researchers discovered that the box jellyfish were using their eyes to keep focused on the tops of the mangrove trees bordering the lagoons where they live.5 I.e., the jellyfish were using their vision to find their preferred habitat (between the prop roots in Caribbean mangrove swamps rich with the crustaceans they eat) and to stay there—even in the presence of strong tidal or stormwater currents.
“This is the first time terrestrial cues have been demonstrated to be used for navigation by jellyfish or any other invertebrate [animal lacking a backbone]”, said Dan-Eric Nilsson, of the University of Copenhagen.6
The researchers say that box jellyfish could even make out the mangrove canopy from a distance of eight metres away (depending upon the amount of surface ripple and the height of the trees). Crucial to being able to do this underwater is the upper lens eyes having a vertically centred visual field of, according to the researchers, “just below 100º, [which] closely matches Snell’s window”.5 Snell’s window is the 97º circular window through which an underwater observer can see the entire 180º of the terrestrial world compressed by refraction as the light passes through the water surface.
Surprise, surprise, surprise
In the conclusion of their published paper in Current Biology, the researchers were refreshingly lucid: “It is surprising to find such a navigational system in an animal as basal as a jellyfish.”5 By ‘basal’, they were referring to its lowly position on the evolutionary ‘tree of life’. They simply could not contain their surprise:
“From an evolutionary viewpoint, the use of terrestrial cues does not seem to be the most straightforward source of information from a marine organism, especially not for a jellyfish.”5
Lead researcher Anders Garm of the University of Copenhagen was widely quoted in the popular media, too: “It is a surprise that a jellyfish—an animal normally considered to be lacking both brain and advanced behaviour—is able to perform visually guided navigation, which is not a trivial behavioural task. This shows that the behavioural abilities of simple animals, like jellyfish, may be underestimated.”7
The surprise was contagious, with University of Texas marine scientist Edward Buskey, on hearing of the study, telling New Scientist, “The discovery of this advanced visual ability in an animal with a primitive nervous system may surprise some. We have an under-appreciation for how sensory systems in simple organisms are used for fairly sophisticated adaptations.”8
‘Under-appreciation’ is right. There is an under-appreciation that so-called ‘primitive’, ‘simple’ organisms are not primitive or simple or ‘basal’ at all. Rather than supposedly showing what eyes were like ‘early in evolutionary time’, the sophistication evident in box jellyfish eyes points to them having been designed that way (right in line with Romans 1:20) for a purpose well suited to the box jellyfish’s specific habitat. Sadly, there is a strong under-appreciation of that Designer.
Box jellyfish use their unique eyes to look out to the world above their watery surrounds. If only evolutionists could look beyond the hopeless darwinian paradigm in which they are so immersed, they, too, might find the navigational clues that all of us need to find our way ‘home’ (Matthew 7:14, John 14:6).
References and notes
- Thompson, A., Jellyfish have human-like eyes, www.livescience.com, 1 April 2007. Return to text.
- Multi-eyed jellyfish casts new light on Darwin’s puzzle, New Scientist 186(2499):18, 14 May 2005. Return to text.
- Nilsson, D.-E., Gislen, L, Coates, M., Skogh, C. and Garm, A., Advanced optics in a jellyfish eye, Nature 435(7039):201–205, 2005. Return to text.
- Facilitated by a heavy gypsum crystal (statolith) embedded in the structures surrounding the eyes. Return to text.
- Garm, A., Oskarsson, M. and Nilsson, D.-E., Box jellyfish use terrestrial visual cues for navigation, Current Biology 21(9):798–803, 10 May 2011. Return to text.
- Through unique eyes, box jellyfish look out to the world above the water, physorg.com, 28 April 2011. Return to text.
- Parry, W., Brainless jellyfish navigates with specialized eyes, www.livescience.com, 28 April 2011. Return to text.
- Weaver, J., Brainless box jellyfish know which way is up, newscientist.com, 28 April 2011. Return to text.