The visceral photophores of the two genera are similar in arrangement but the branchial photophores are much larger in Pterygioteuthis (left illustration), and the anterior abdominal photophores in Pyroteuthis (middle illustration) consist of three photophores rather than one.
Figure. Left - Immature Pterygioteuthis microlampas. Middle - Mature female Pyroteuthis addolux. Right - Labeled diagram drawn from the Pyroteuthis photograph. Note the difference in the sizes of the oviducal glands suggesting that only the right oviduct is functional. The most posterior abdominal photophore of Pterygioteuthis and the two most posterior abdominal photophores of Pyroteuthis are not within the bounds of these photos.
Figure. A closer look (photomicrographs) at the visceral photophores of Pterygioteuthis (left to right: branchial, anterior abdominal, anal photophores) shows that the major photophores have very different structures. In Pyroteuthis the branchial and anterior abdominal photophores appear similar in structure (see top photo).
