Nucleus-Sharing Shev
The nucleus-sharing shev diverged from its ancestor by emerging into the shallow seas around Wright. It maintained nearly the same lifestyle but adapted for a more populated and high-energy environment.
Like all shevs, the nucleus-sharing shev consists of very large cells, which are able to operate at great size due to containing numerous nuclei. They have shrunk slightly in response to the decreased pressure in the shallows making it harder to maintain the necessary internal pressures. Each cell grows a substantial shell, useful both for defense and to support the cell's contents. They've developed the ability to produce aragonite, which now comprises significant layers in their shell, along with whatever minerals they're able to pick up in their environment. These shells often contain relatively high levels of heavy metals too, making them particularly dangerous for predators to snack on. The layers of aragonite make the outer shape of the shell look a bit different; the irregular bricks are still present but smoothed over by the aragonite deposits, resulting in gentle waves over the underlying blocks.
Each cell has an array of pseudopods that face upwards, used for filter-feeding. These have become even thinner, as they now focus on picking up greater quantities of smaller food, now that they are in an environment with relatively more directly available food. When under attack, these pseudopods can retract most of the way into the thick shell. Furthermore, some pseudopods become repurposed, as the organism develops in its lifetime, into spikes, as minerals and aragonite grow over them, leaving a pointy barb at the end and making for a nastier experience for any predators.
Like the ancestral brick shev, individual cells link with each other to form larger "reefs." Each cell has leg-like pseudopods at the base, useful for moving across the sea floor. These hook up with other cells' shells and fuse them together. Once linked, these shells gradually fuse together through slimy "mortar." Unlike before, they retain some mobility, as the base of these pseudopods extends below the organism, but this only allows them to creep slowly over the course of many days. It is still possible for cells to latch on above fellow cells, causing the lower layers to die and leading to a reef building upward, but this mobility makes it more possible to get away or to move out of an unsuitable or constrained environment. They tend to grow across more than upward, so while they typically reach 25 centimeter diameters (this is an average, not a maximum), they often have much fewer layers vertically. But they do start to stack as generations go by, and they'll still die after a few decades, however, which can result in reef structures of up to a meter littering the ocean floor.
Nucleus-sharing shevs have very little in the way of sensory equipment, mostly just feeling with its pseudopods and detecting dissolved chemicals in the water. This is enough to let them turn away from barriers, retract under attack, and reach out toward food. They don't really have any other way to deal with threats, though; their armor is their bulwark.
To enhance genetic diversity so as to respond better to the highly changeable conditions, the nucleus-sharing shev is now able to exchange nuclei between conjoined cells, which they transfer using the linking pseudopods at their bases. Multiple nuclei within a cell can easily exchange genes with each other. This exchange also keeps cells within a reef more genetically similar to one another. Reproduction itself occurs by budding off a new cell from one of the pseudopods, as the shells make it too difficult for the cells to simply split.