Monognathidae

Monognathidae is a small family of deep-sea jawless fish belonging to the order Saccopharyngiformes. These fish are characterized by their highly specialized anatomy, which is adapted for a pelagic, predatory lifestyle. The most distinctive feature of Monognathidae is the single, elongated barbel that extends from the chin, which is believed to be used as a lure to attract prey. They possess extremely large mouths relative to their body size, lined with sharp, backward-pointing teeth. Unlike many other fish, Monognathids lack pectoral and pelvic fins, and their dorsal and anal fins are reduced to small, fleshy ridges. Their bodies are typically elongated and eel-like, and they lack scales. The eyes are also greatly reduced or absent, consistent with their inhabitation of the aphotic zone. Little is known about the reproductive biology or life cycle of these elusive creatures. They are rarely encountered and are primarily known from specimens collected in deep-sea trawl surveys, suggesting they inhabit the bathypelagic and abyssal zones of the world's oceans. The family currently contains a single genus, Monognathus, with several described species, though further research may reveal more.