Anglerfish are a bony fish that arose 130 million years ago; long enough to have adapted to a wide variety of habitats, and so have a worldwide oceanic presence.
Different anglerfish do their angling at different depths. Some live on continental shelves. Most are deep-sea denizens. What unifies anglerfish is a fleshy growth (illicium) from the head that acts as a lure (esca).
Only female anglerfish have illicium. Much-smaller males live solely to find a mate, to which they attach and provide a continuing sperm supply, fed by their mate as compensation. Those males that fail in their life mission quickly die.
The illicium is a modified dorsal fin. Dorsal fins typically stabilize fish: preventing unintentional rolling and assisting in sudden turns. In anglerfish, the illicium acts as a fishing rod.
In deep-sea anglerfish, at depths where sunlight does not penetrate, an esca is bioluminescent. This little light lures small fish upon which the anglerfish preys, and as well advertises for mates.
The source of anglerfish luminescence comes from colonies of symbiotic bacteria that dwell in and around the esca. Some bacterial species only light up when fed by the fish, which provide the vital food ingredients for the bacteria to luminate.
Esca precisely strobe on and off based on anglerfish control. To accomplish this, an anglerfish communicates with its esca bacteria energetically, as chemical communication would be too slow to signal the millions of luminescent symbionts to act synchronously at sufficient speed.
The anglerfish is one of innumerable examples of intricate symbiotic adaptation that only be explained teleologically, and, in the instance of anglerfish, with interspecies communication links that are beyond purely physical means.