Anglerfish

Many species have specialized shapes and organs that aid them in hunting and feeding. Among such fishes are the female anglerfish, which lies on the ocean bottom and presents a small, wormlike knob of flesh called the esca on the end of a long spine as a bait to other fishes.

Striped anglerfish (Antennarius striatus)

Anglerfish light the esca with bioluminescence (their own light) and then wiggle it to mimic a small marine animal. When other creatures come to eat the small marine animal, the anglerfish eats them. 

They are called anglerfish because they catch fish with bait, just like anglers, who use a rod and line (rather than nets).

Most species of anglerfish have large heads that bear enormous, crescent-shaped mouths full of long, fang-like teeth angled inward for efficient prey grabbing. They're able to swallow prey up to twice as large as their bodies.

Only female Anglerfish have escas and actively look for food. The males are tiny and spend their entire life finding and fusing to female Anglers, where they begin to degenerate until they are little more than a pair of gonads providing sperm to the female on her command.

Because of the vastness of the deep ocean, when a male and female anglerfish mate their bodies fuse into one. The male's now useless body parts like eyes and fins wither away. He spends the rest of his life attached to her like a parasite, taking food and providing her with babies.

The spawn of the anglerfish consists of a thin sheet of transparent gelatinous material that floats free in the sea. The larvae are free-swimming and have the pelvic fins elongated into filaments. The egg mass of the anglerfish covers an area of 5.6 to 8.4 sq m (60 to 90 sq ft).