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A creature with a built in flashlight

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I know things like flashlight fish exist; things with luminescence and all that. But how strong could the light be?

I have this cave dwelling species with three eyes except the middle one isn't exactly an eye but a place that can create a beam of light like a flashlight so the creature can see. It can be turned on/off and the intensity can be adjusted. This creature also comes above ground on occasion.
I thought about just giving it echolocation, but then the three eyes would not be as needed, and the three eyes thing is sort of linked to their triangular architecture and other culture things. How strong of a light can be created biologically, and how?

Or, would having three eyes still be realistic if it also has echolocation?

(Okay, this is a bit embarrassing, but not long after I posted this I realized that giving it a horn for the third point for a triangle themed face would solve all my problems so now my anxiety has flared up cause I asked for help I no longer need and took people's time for nothing)

Why should this post be closed?

This post was sourced from https://worldbuilding.stackexchange.com/q/177083. It is licensed under CC BY-SA 4.0.

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2 answers

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If it's ancestors have 3 eyes and there are no pressures for it to loose one, then it's completely plausible for it to keep them.

Just look at bats. Though they are somewhat poorly developed in a few species (not the rule though, as many bats see decently well, with flying foxes having notably good vision). So if your creature leaves the caves, it will need eyes, unless it also starts to rely on echolocation outside the caves.

Dolphins too are a good example, although they still use their vision, underwater isn't the best place for light to travel compared to air, so to make up for it, they rely on echolocation to find prey, as well as other functions.

Now the flashlight. We have some instances of bright bioluminseclscence, but even the brightest instance (a group of dinoflagelates from Mosquito Bay) clearly don't shine as bright as a flashlight. Additionally, to he able to get something brighter, your 3rd eye will likely have to convert into something less useful at seeing, as it'd need to adapt to become a lightsource.

Additionally, I don't think it'd be an advantage overall. Sure it can see in the dark due to having a flashlight attached to it, but unless it's the only thing with eyes inside the cave, both prey and predator will always be able to see it coming. So yeah, overall echolocation sounds a bit better as an advantage.

Summing up: can it happen? Kinda, angler fish and many abyssal species use it, though more as a lure than as a flashlight, and it won't be nearly as bright as one. It just seems like just adapting it's eyes to be better at seeing in the dark (having a tapetum lucidum for example) and giving it the ability to echolocate, thus granting it 2 ways to navigate, sight when there's enough light, and echolocation for when it finds itself in very dark environments (or should its eyes be wounded/rendered unusable for a period).

This post was sourced from https://worldbuilding.stackexchange.com/a/177086. It is licensed under CC BY-SA 4.0.

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There is a nice lecture on bioluminescence at

https://www.youtube.com/watch?v=a04AZ0jMjx4

At around the 11 minute mark they have a video of fish with an organ where it can turn the bioluminescence on and off and direct the light.

Fish with Bioluminescence

As you can see from the photo the light is not that directional. The direction is improved some by the organ having a reflective pigment at the back and the bacteria producing the light in the cavity of the organ having the reflected light directed forward.

In a completely dark environment like a cave even a small amount of light could be useful. Perhaps as a lure, or to provide some background light.

However, there are several examples of animals evolving to lose their eyes as they adapt to a cave environment.

This post was sourced from https://worldbuilding.stackexchange.com/a/177101. It is licensed under CC BY-SA 4.0.

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