Attheya longicornis vs A septentrionalis

Has anyone the literature for distinguishing A. longicornis and A. septentrionalis?
In Throndsen, Hasle and Tangen "Phytoplankton och Norwegian coastal waters" they distinguish it by the ratio between apical-axis and length of horns.
But in this database we cite another source using a different character.
I append this species, which I presume is Attheya longicornis before publishing to the database.