Gulf hagfish

The gulf hagfish (Eptatretus springeri) is the only known species with the ability to enter brine pools, or pools of extremely high salt content, unharmed. These pools resemble lakes on the ocean floor. They exist in both the Gulf of Mexico and the Mediterranean Sea. The high salt content, approximately 200 ppt compared to 35 ppt for standard seawater, creates a buoyant surface which renders oceanic submersibles unable to descend into the pool. Often, other species can be seen floating lifelessly on the surface. It is believed that the pools only support bacterial life.