Golding's use of light imagery in this scene leads to a tone of gentleness. He describes how the water "dressed Simon's coarse hair with brightness" and the "moving patch of light" made by the phosphorescent creatures. Then Simon's body essentially becomes art:
The line of his cheeks silvered and the turn of his shoulder became sculptured marble. The strange attendant creatures, with their fiery eyes and trailing vapors, busied themselves round his head. The body lifted a fraction of an inch from the sand and a bubble of air escaped from the mouth with a wet plop. Then it turned gently in the water.
Some have suggested that this is Christ imagery as well. whether or not you agree with that, there's definitely a sense of Simon becoming more than a dead body. He is lit up by the "strangely attendant" creatures, implying that they recognize he should be taken care of in some way. Also, the movement in the water may suggest a transcendence of death.