Last trip to the LFS I actually seen bumblebee shrimp hosting them in the holding tank. Although I never heard of bumblebee shrimp hosting these and I know they like tubefeet similar to harlequin shrimp.. so that may need some experimenting..
Gnathophyllum panamensis I believe eat asterina starfish only similar to bongo shrimp. Bumblebee shrimp will attack tubefeet if offered but not required as they'll also scavenge off other things unlike harlequins. Harlequins won't host anything other than their prey starfish during feeding.
I bought them on impulse cause they pop up at my LFS here in Australia and i thought they were cool. Didn't realize they required a host.
They just hung out with my sun coral 24/7 sitting in between the polyp tubes or crawling around the base.
When i added an urchin they started hanging out with that, chilling in between the spines following where ever it went.
Then one day i saw one of my fairly large hermit crabs fall of a rock and had it's shell opening facing skyward, and there were the two emperor shrimp chilling inside the hermit crab shell with the hermit.
As far as i know since i saw them last month, they're still chilling and living inside the shell of this hermit crab with the hermit........ weird.