Sea Drops: Every time a member of a certain species of bacteria divides, the new cells spread apart, yet remain attached through the slimmest of fibers. This branching continues as the colony grows. Oceanic zones rich in these floating colonies is rather gelatinous, as the colonies stick to each other. When threatened by grazers, the colonies shrink, each bacterium pulling in its fibers. Water is expelled and the loose, branched colonies coalesce out of the gelatinous sea to become tiny, dense, hard spheres that sink to the seafloor out of reach. After the threat has passed, the colonies spread out again and absorb water. The production of gas vacuoles in each cell raises the colony back up to the surface.
Pressure Plants: Some autotrophs trap gases bubbling up from the seafloor. The release of these gases through special valves produces usable energy for the organism. This is a variation on an idea I had long ago for organisms that rose and fell with the currents in an atmosphere, took in high pressure gases, and released into zones of low pressure. I have several body forms in mind, but I can't go into them right now. Some of these autotrophs also absorbed light from the sun to generate heat to produce internal pressure in specialized tubes.
Trick-Date Tree: This tree has hollow structures resembling pitted dates. Insects are lured inside and get stuck where they are digested.