Abyssal Clumpstar
Clumpstars continued their descent into the ocean depths, at last extending far into the abyss. There, they have adopted a slow-growing, long-lived lifestyle. The adults simply feed on whatever marine snow falls upon them, growing in clumps much larger than their ancestors. Their feeding hairs are about the same size as before, making them relatively much smaller on their bodies. Otherwise, the adults are much like a subdued, almost dormant-seeming version of their predecessors: They have star-shaped bodies with four arms, which fit within a communal calcite shell.
Their life cycle has one substantial change, however. In midnight clumpstar, clumps only formed in adulthood, whether by a larva joining an existing clump or, more commonly, asexual fragmentation. In abyssal clumpstar, however, they begin forming clumps in their larval stage. These larvae are free-swimming and lack shells at the beginning of their life. As swimmers, they are better able to find other larvae, mostly using their hairs to sense vibrations, though they also have rudimentary vision (their eyes are lost upon adulthood). Once they find each other, larvae will clump together, clinging to one another using the same cellular baits that the adults use to cling to their shells. Larvae can also fragment, each arm developing into a new larva. If part of a large group, these fragments will disperse; otherwise they will stick together.
Once a clump of about five has formed, the larvae secrete their communal shell, which they will dissolve and recreate a few times as they grow. This leads to a life stage that somewhat resembles nautstars, but with many more tentacles and a very different internal anatomy. Once a clump gets closer to adult size, they sink to the ocean floor and enter adulthood, losing their ability to fragment, and beginning production of gametes for spawning.
Abyssal clumpstar has developed a full stomach pouch, just past the mouth, but it lacks any kind of through-gut, so they excrete through the same opening. Their neural system remains simple, merely a nerve net without even ganglia. They have a heart just below the stomach, pumping blue blood throughout the organism. They breathe through long, thin, flimsy gill tentacles, ancestrally derived from feeding hairs.