Ironcrab Bladestaff

In deep undersea trenches there live giant crabs, the smallest as big as a Triton child with the largest crawling the floor of the ocean as whale sized leviathans. They gain almost all of their sustenance from creatures that feed on enormous geothermal vents. They are known as Ironcrab Crawlers. 
Due to the amount of minerals in their diet, their shells are a incredibly durable mixture of metal and chitin that makes for an light but strong material with which Triton can make weapons and armor.
Ironcrab weapons and armor are prized by the Triton, hard to find and even harder to kill the weapons are the most common among the Triton and almost unheard of on the surface.
The weapons can take many forms, some maintaining the clean lines of the straightest parts of the exoskeleton while others create naturally curving and nodular weapons that take the strangest and most organic shapes that the shell offers. Still others will layer the chitin into plates that form powerfully defensive weapons while maintaining much of the cutting power that the material offers. 
Working the material is a hard process and a closely guarded secret of Triton artisans, The weapons keep a good edge but require training to maintain and sharpen without damaging the chitin. 
The Ironcrab Bladestaff is a well known weapon among the Triton and one that is considered hard to even learn much less master. A wielder of this would be well regarded among other martial individuals, it is well suited to combat on either land or sea. Royal guards will often bear these weapons. 
Two long blades, often straight, are attached together with a long handle that allows a skilled user to thrust, parry, spin and otherwise utilize the best benefits of both blade and staff with an additional option of disconnecting the blades and using them as dual swords.

Two-Handed Weapon, finesse, Light 1D8(+1d6 with a second strike)
Dual-blades attached together with a long handle, a proficient user can make a second attack as a bonus action as long as the blades are connected. If a proficient user does NOT make a bonus attack, they can treat the additional blade as though they have a shield granting +1 to their AC.
As an action, the user can disconnect the blades and use them as two individual swords, losing the AC bonus but allowing the off blade to do 1D8 damage instead. It takes a full action to connect them again.