It is 620 million years ago. A terrestrial planet eight tenths the size of earth orbiting a G class star has just gone into a massive ice age. There is almost no liquid water on the surface. it is cold and lifeless. Except in the caves. Massive hydrothermal vents spout chemicals into the surrounding water, which is consumed be chenophoric bacteria. The vast amount of heat created by these vents has enough power to separate oxygen from hydrogen in water. The vast amount of oxygen created allows for aerobic respiration in organisms causing an explosion of biodiversity.

The sea candle is a sessile monosomal creature. It extends ts respiration/feeding tentacles into the water to filter chemotrophic plankton. It will periodically pull its feeding tentacles into its gut for digestion. It has four sensory tentacles that extend from its gut,when disturbed it can retract its feeding tentacles to avoid predation. As it grows it absorbs minerals to grow a primitive shell around itself. In its larval stage it will float with plankton before descending to the rocks to become an adult.