Synauchenia

Synauchenia coalescens is a trout-sized, highly compressed arthrodire placoderm restricted to the Late Frasnian-aged Kellwasserkalk Fauna of Bad Wildungen.
"S. coalescens" is unique among arthrodires in that the head shield and the trunk shield are fused or "firmly sutured" together in an immobile, helmet-like unit. The neck gap is absent, and the articulations between the cranium and thorax are lost in the evolution of this peculiar feature. The skull of the holotype is 10 cm long.
"S. coalescens" was originally placed in its own family, but, it was later determined to be closely related to "Oxyosteus" and "Brachydeirus", and accordingly placed within Brachydeiridae.