Many years ago, I kept a pair of Gnathophyllum that I caught locally near Sydney. I suspect they were G. taylori, which at the time was not described. They were in a tank by themselves, but I ended up having to add a dottyback (Oxycercichthys veliferus) and couldn't find the shrimp to move them on to a different tank. Dottybacks are notorious shrimp predators, so I assumed I would never see the shrimp again. Months later, however, I was surprised to find the pair holed up in the dottyback's cave. The dottyback was ignoring them. I never followed it up to see why the dottyback didn't eat them, but suspect they are either toxic, or perhaps act as parasite cleaners.