Odobenidans were a species that Jo Grant thought resembled a walrus.
An Odobenidan spaceship became trapped in a cavern under Earth's Mediterranean Sea. The Master, who was trapped in a time loop in the same area, tried to free them using earthquakes. The Odobenidans became trapped in the time loop too. During most of the time Jo and the Third Doctor were in the cavern, the Odobenidans were unable to notice them, due to the effects of the time loop. (PROSE: The Seismologist's Story)