Tentatively *Polymephycite tympanum*. Not animal, plant, or fungus, but a fourth category of complex life analogous to Earth protists.
1. Central structure The central stipe is a biopolymer akin to chitin or keratin held upright by a beard of air-filled sacs (pneumatocysts).
2. Dual feeding strategy Photosynthesis is the primary nutrient source, but cave-dwelling drums subsist on dissolved nutrients.
3. Reactor glow Adults develop a large bioluminescent swelling called a sprangia. Its blue light precisely mimics the Cherenkov radiation of a nuclear fission reactor immersed in seawater.
Assessment: further investigation required. Await further updates.