I've been troubled by helmets recently. Namely, artwork of Horus leading the Sons of Horus into battle. The image shows all sorts of variations of space marine helmets ranging from the Mk4 helmet to the Mk6 helmet. This marine sitting in the bottom corner caught my attention though:
I don't recognize the helmet that they are wearing at all. At first I thought it was like the helmet the khornate berzerkers wear (like below)....
....but quickly realized the differences and that even then, I don't actually know what type of helmet the berzerker wears.
Neither helmet appears in the different Marks of Space Marine power armor (seen below).
What version of power armor do these helmets belong to or are they their own little special version?
Bonus: Do they offer the user anything special compared to other helmets?