A genus of bacteria that are parasites of mucous membranes. Subgenus Moraxella is characterized by gram-negative rods that are often very short and plump, frequently resembling a coccus, and usually occurring in pairs. Subgenus Branhamella has gram-negative cocci occurring as single cells or in pairs with the adjacent sides flattened. They are usually harmless parasites of humans and other warm-blooded animals and are generally considered not to be highly pathogenic. Most species may be opportunistic pathogens in predisposed or debilitated hosts.