A Flagisallus is a type of large fish found on Lantea, capable of surviving at oceanic depths well below 350 meters. Due to their appearance, members of the Atlantis expedition have taken to identifying the creatures as whales, but the creatures are not mammalian. They do, however, seem fairly intelligent and possess a form of language.
Flagisallus are capable of projecting auditory and visual signals; the Ancients constructed a device that could facilitate communication with them, and attempted to teach the Flagisallus their own language. The flagisallus stored several details of at least one event in their genetic memory, using it to warn the Atlantis expedition of an impending coronal mass ejection. They are also sensitive to changes in the solar magnetic field.
The species communicate with their own echo location by using low frequency sonar, amplified by an EM field, creating vibrations that can be uncomfortable to humans. In one case, it has shown that it can kill a human.