Feather dusters will eat most any detritus,bacterioplankton,or phytoplankton.They select/reject foods based on micron size.Particle size of foods for these should be less than 30micron(phyto is about5-10micron).Xenia and the majority of zoanthids are nearly autotrophic,they rely on photosynthesis as the primary method of obtaining nutrition.There are some zoanthids that accept planktonic foods but finding out which ones accept what kinds of foods is trial and error.Xenia do not rely on capture,they use absortion for feeding and uptake dissolved nutrients out of the water column.SPS type corals do use active capture.The foods they eat are animal based,not plant(phytoplankton).Once again,they capture foods based on there micron size,50-125 micron is about idea for many SPS coraals.