Unfortunately these males are rarely seen. As a result, separation of this species from Japetella diaphana depends largely on the differences in eye size and length of the optic stalks. However, with isolated specimens, the difference is not as obvious. The problem is accentuated in larger Japetella where the eyes are removed from the brain and a distinct optic stalk is present. Note that in the Bolitaena pictured here the distance from the eye to the brain is several times the eye diameter.
Females develop a ring-shaped light organ around the mouth.
Brooding females, however, are found near 800 m off Hawaii. The early paralarvae of Bolitaena pygmaea have an abundance of chromatophores that easily separates them from Japetella diaphana if specimens are intact which they usually are not. Note also, that the optic lobe of the brain is distinctly separated from the brain by a short optic stalk. In Japetella diaphana paralarvae no such separation is apparent. The life history appears to be very similar to that of Japetella diaphana .