Saccopharyngidae

Saccopharyngidae is a family of deep-sea fish belonging to the order Saccopharyngiformes. Members of this family are characterized by their elongated bodies, large mouths, and absence of scales and pelvic fins. They are often referred to as "gulper eels" due to their remarkable ability to swallow prey much larger than their own heads. This is facilitated by their distensible jaws and stomachs.

These fish inhabit the mesopelagic and bathypelagic zones of all the world's oceans, typically found at depths ranging from 500 to 4,000 meters. Their diet consists mainly of smaller fish, crustaceans, and squid. Little is known about their reproductive habits, but it is believed that they are oviparous, laying eggs.

The family Saccopharyngidae currently contains two genera: Saccopharynx and Eurypharynx. Saccopharynx species are generally larger and possess a distinct, whip-like tail. Eurypharynx, on the other hand, has a more evenly proportioned body and a more rounded tail. Both genera exhibit bioluminescent organs, though their precise function is still under investigation, with theories suggesting roles in prey attraction, communication, or defense. Due to their deep-sea habitat, Saccopharyngidae are rarely encountered by humans and remain a subject of ongoing research.