Clumpstar
The clumpstar evolves from reefstars that spread deeper into the ocean. With the decrease in available energy, they are unable to sustain reefs there, but they retain the ability to secrete communal shells. They are typically found in clumps of several individuals.
The individual body plan is little changed: a central body with four limbs, with the middle attached to the shell by modified baits and the arms extending above. The arms are covered in thin baits used for filter-feeding. These are also able to extract oxygen from the water, but some of them have now grown into longer feathery filaments that serve as specialized gills, thus better coping with their larger size and reduced oxygen. Each arm also has an eye at the end; these have increased in size due to the dimmer light.
They can reproduce by fragmentation, in which one arm at a time detaches and grows a new body. This will usually settle next to its parent, increasing the size of the clump, unless the clump is already very large. As a result, clumps often consist mostly of genetically identical individuals. They can also spawn spore-like gametes, which will produce free-swimming larvae when fertilized, which eventually form their own shells and sink to the ocean floor. Sometimes, larvae may join on to a new clump, but they will usually settle into an independent existence.
Internally, they remain fairly simple. Most of the body is undifferentiated tissue, but they have a neural network to coordinate their senses and communications, which they do by releasing chemicals into the water, allowing them to warn each other. They retract into the shell when under threat by predators. They absorb nutrition directly through their filter-baits, but they also have the beginnings of storage tissues.