Measuring only about a foot and a half long, the lanternshark may seem distinctly less impressive than its larger shark cousins. But this diminutive fish has mastered the art of bioluminescence, concealing themselves from prey while challenging any potential predators.
Because they are deep-sea fish, it's not surprising that lanternsharks have bioluminescent abilities, but they are one of the rare species that can put this adaptation to use in multiple ways. On their bellies, the lanternshark has light-producing photophore cells, which produces light that is visible to the fish swimming beneath it. These are usually prey, as Dr. Julian Claes of Belgium's Catholic University of Louvain explains to the BBC:
"Imagine you are below the shark, the shark is swimming and you have the light from the Sun coming down. If you are just below the shark what you are going to see is a shadow. So imagine if the shark can actually produce a light, which is identical to the light produced by the Sun. Then the shadow of the shark is going to disappear."
That trick allows the lanternshark to make quick work of unsuspecting prey, but what about the lightsabers I promised in the headline? Well, that's what Claes and his fellow researchers refer to the two hard spines that just out of the lanternshark right in front of its two dorsal fins — you can see them both in the photo up top. Those spines are positioned by another set of photophores, which cause the sharp spines to glow in a way that is similar to but (if the lanternshark knows what's good for it) legally distinguishable from the iconic Star Wars weapons. Dr. Claes explains further:
"It was surprising - why would you try to be invisible from below but visible from the dorsal side? It's a way to say: 'Don't bite me, I'm dangerous, I have spines on my back. You could be hurt.' When you live in this dark place, what you try to do is avoid is to be seen by other animals, because there are no places to hide. It can be very dangerous - you put yourself at risk when you produce light from your back, unless it acts as a warning system. It's surprising that these two apparently opposite behaviours can occur in a single organism at the same time. It is really paradoxical."
For more, check out the complete original paper at Scientific Reports.