Lure (Illicium)

The illicium (from Latin: "lure, enticement") is the elongated first dorsal fin ray of anglerfishes (Order Lophiiformes) that has migrated forward to the snout and is tipped with an esca (bulb) containing bioluminescent bacteria. The esca glows blue-green in the darkness of deep water, mimicking small prey to attract larger prey within striking range of the anglerfish's enormous gape. Different anglerfish species have evolved esca of different shapes and bioluminescence patterns, and the structure of the illicium and esca is the primary character used in species identification within the group.

Female deep-sea anglerfishes can have an illicium three times the length of their body. Male anglerfishes (much smaller) have no illicium — they parasitically fuse to females and provide sperm in exchange for nutrients.