Ceratioidei

Ceratioidei is a suborder of deep-sea anglerfishes. These fish are characterized by extreme sexual dimorphism, with the males being much smaller than the females. In many species, the male fuses himself to the female, becoming a parasitic sperm-donor. They inhabit the bathyal and abyssal zones of all oceans, at depths ranging from 200 to 5,000 meters.

The most striking feature of ceratioids is the illicium, a modified dorsal fin spine that projects from the head and bears a bioluminescent esca. This lure is used to attract prey in the dark depths. The esca is produced by symbiotic bacteria and can be illuminated intermittently or continuously.

Ceratioids exhibit a wide range of body shapes and sizes, though most are relatively small, with females typically ranging from a few centimeters to over a meter in length. Their coloration is usually dark, ranging from brown to black, which helps them camouflage in their deep-sea environment.

Reproduction in ceratioids is a unique and challenging aspect of their life cycle. Due to the scarcity of mates in the vast deep sea, males often rely on detecting pheromones released by females. Once a male finds a female, he bites into her body and fuses with her circulatory system, becoming dependent on her for nutrients. He then loses his eyes and internal organs, except for his testes. This parasitic relationship ensures that the female always has a readily available mate.

The diet of ceratioids consists mainly of smaller fish and invertebrates, which they ambush using their bioluminescent lures. Their large mouths and expandable stomachs allow them to consume prey larger than themselves. Despite their fearsome appearance, ceratioids are not considered a threat to humans due to their deep-sea habitat and small size.