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, while others believe them to be opercula (mandibles). It may have had a function similar to the head shield of modern nautiluses.