Strange Anglerfish has its own light source
The strange anglerfish lives and feeds deep down in the seas and oceans where it is virtually pitch black. With a modified fin that hangs out in front of it, it has its own light source at the bulb at the end of that fin. But its purpose is not for lighting the fish's way around in the dark. Instead, it is used to lure prey. The anglerfish can wiggle the light around like bait. Other marine animal that thinks the light is food will gravitate towards it like moths to a light.
Once the prey comes close enough to touch the anglerfish's tentacles, the anglerfish's mouth reflexively closes and it is an easy meal for the anglerfish snap up the prey in its mouth, which have long sharp teeth -- making them look like scary monsters of the dark sea.
Video of Angler Fish Eating a Goldfish in One Gulp
Source of the Anglerfish light
The light is produced via bioluminescence by a small organ at the tip of the fin. Bioluminescence means light produced by living organisms. In this case, it is produced by millions of bacteria that fills the small organ.
How the anglerfish come to harvest all these bacteria is unknown. It has been speculated that the bacteria from seawater can come in through small pores.
Anglerfish gets even stranger
Anglerfish comes in a wide variety and they are members of the order Lophiiformes.
If you think having a fishing rod structure coming out of the head with a bulb at the end that lights up is strange, then the mating habits of the ceratioid group of anglerfish is even stranger.
In this type of anglerfish, the male is much smaller than the female. See that parasite looking creature that hangs from the bottom of the female anglerfish on the right? That is the male.
The male have extremely good sense of smell and can detect the pheromones of females. Right after birth, it immediately seeks out the closest female.
Wikipedia says ...
"When he finds a female, he bites into her skin, and releases an enzyme that digests the skin of his mouth and her body, fusing the pair down to the blood-vessel level. The male then slowly atrophies, first losing his digestive organs, then his brain, heart, and eyes, and ends as nothing more than a pair of gonads, which release sperm in response to hormones in the female's bloodstream indicating egg release. This extreme sexual dimorphism ensures that, when the female is ready to spawn, she has a mate immediately available."
The male actually becomes fused permanently into the female.
How does nature come up with such creative schemes?
It may be hard to believe. But to make sure that someone is not just making things up on Wikipedia, your can reference and read about this strange reproductive process known as "sexual parasitism" on the site Nature.com linked here. where it says the female becomes "a kind of self-fertilising hermaphroditic host".