danfrith,
The Crinoid squat lobster Allogalathea elegans does very well long term without a feather star host. They will find an area under ledges of the live rock, soft corals, and even anemones in the home aquarium for protection. These crustaceans use the feather star in the wild in order to move through the water in search of food. In captivity they will feed on a variety of meaty foods such as mysis shrimp, brine shrimp, and other particles of food in the water column.
Joyce F.
LiveAquaria
Drs. Foster & Smith