A genus of motile, aerobic, facultatively anaerobic, coccoid bacteria (family Streptococcaceae) that occur singly or in pairs, with flattened adjacent sides. They are gram-indeterminate but have a cell wall like that of gram-positive bacteria, and are parasitic in mammals. The type species is Gemella haemolysans, which is found in bronchial secretions and in mucus from the respiratory tract. [L. dim. of geminus, twin]