strange axle nut on 5th wheel hub

Hello all, first time poster.
I have a 2010 28RKBS Wildcat that I am trying to repack the wheel bearings on and ran into a problem. It has what looks like a large nylon locknut
with no normal castle nut and retainer. Also inside there looks to be a snap ring. has anyone else ever seen this used? Any help would be appreciated. thank you.