These creatures use their luminoscity in different ways. Some flash their lights on and off to attract a mate. Others lure their prey within striking distance with special glowing appendages that look like worms or other food. Some actually scare predators off with their special luminescent abilities. These vent communities are unusual because a great number of animals live in a very small area surrounding hydrothermal vents.
Hydrothermal vents are cracks in the Earth's crust which spew out hot, mineral-rich water.
The animals that live in vent communities are different from most other deep sea floor animals in that they don't scavenge remains drifting down from the ocean's upper zones, but rely on the hydrogen sulfide-eating bacteria for their food. They also tend to grow very fast, and can become rather large. Sea anemones filter the bacteria from the water.