Gnathodoridoidea is the most basal group of dorid nudibranchs. They are characterized by havin a diaulic reproductive system and other plesiomorphic characters in the digestive, circulatory, renal and nervous systems. Only a few species, belonging to the genus Bathydoris, are known, all of them from cold waters in the artctic, Antarctica and the deep-sea. All gnathodoris are omnivorous.