Complex sentence: Some authors consider the aptychus to be a jaw apparatus (mandibles), while others believe them to be paired opercula, thus aptychi may have had a function similar to the head shield of modern nautiluses.
Split into simpler sentences: Some authors consider the aptychus to be a jaw apparatus (mandibles), while others believe them to be paired opercula. If the latter is the case, then aptychi may have had a function similar to the head shield of modern nautiluses.