Fixed Jellyfish - Cladonema
This little guy is in the Jellyfish family - Cladonema jellyfish. Brad mentions: "It is extremely tiny, maybe 1 or 2 mm across, and stuck to my glass (aquarium wall)." I won't go as far as to say it is Reef-safe, but it is interesting none-the-less.
From this page: "These are small jellyfish that can swim, but which also fasten to the substrate. Unlike the Staurocladia mentioned above, they don't crawl much. Not much is known about their biology. In aquaria they probably feed on small copepods and particulate material in the water. They may be distinguished from Staurocladia by more developed globular bell, their slightly larger size, and the shape of the tentacles."
Photo by Brad Benefield