 It is often difficult to superficially distinguish between male and female bigfin reef squids . Some authors say that females are generally smaller than males , but this distinction is not observed in other studies . Closer examination of sexually mature specimens , however , will usually distinguish males from females by the presence of the hectocotylus on the fourth left arm in males , and the nidamental glands and the pale ovaries within the mantle in females . Males also purportedly show a more conspicuous pattern of transverse streaks on their dorsal side . 
