Lithogania
This descendant of the rectangulogania became purely free-floating, abandoning its rectangular shape and in turn the ability to form dense mats. Such an adaptation was no longer the best solution for predation. Instead, the lithogania has adapted by evolving the unique ability to polymerize the dissolved silicic acid in the water. This forms crystals of hydrated silica, which are then deposited as small phytoliths embedded in the cell wall.
Being covered in what are essentially tiny glass shards, these organisms are hard to digest, and their phytoliths can last for many years after their death. They can even cause minor damage to the digestive systems of some filter feeders, if enough of them have been eaten. Billions of dead lithogania sink to the bottom of the sea every year, causing large amounts of fine sand to build up on the ocean floor. This dramatic impact mirrors Terran diatoms, which make up around half of the ocean’s biomass and take up 6.7 billion metric tons of silicon each year. While lithoganians are not quite that successful, they are still an abundant and diverse group, being found in almost every marine environment.
Individual species are often hard to tell apart. Phytolith size and shape vary. The cell itself is usually elliptical, though some members show a weakly rectangular shape, reminiscent of their distant ancestors. Most species live close to the surface, though the number of photosynthetic organelles can vary. Polar species usually have smaller or fewer phytoliths in order to conserve energy and time. Size also varies, but bigger species are more common. While most species have exactly two central vacuoles, a few species have lost the second one in order to make room for other organelles.