Swimming Clumpstar

Over time, the abyssal clumpstar's larvae had been getting more viable, already capable of forming clumps in their free-swimming stage. Some further evolved to begin spawning at that stage, then lost their sessile form altogether, instead growing into a larger swimming clump.

The resultant clump was imbalanced and a clumsy swimmer, but their overall shape soon shifted. Now that they no longer attached to the ground, the former "bottom" of their shells could attach to other shells' bottoms, resulting in a symmetrical clump with two sides. They also became more elongated and sleeker. They still aren't adept at swimming, moving by the beating of tentacles, and they weren't very streamlined yet. Most of the time, they just drift around or even pull themselves across the seafloor using their tentacles. Being slow, their main response to hazards is to retract within their communal shell.

While swimming clumpstars bear some resemblance to nautstars, even sharing the use of hemocyanin with several large nautstars, their internal anatomy evolved almost entirely separately. Each polyp has a stomach behind an opening in its center, which mostly serves as an anus but can serve as a mouth. A single heart lies beneath this and pumps blood throughout the body's open circulatory system. They breathe through long filamentous external gills. These gills are homologous with the small feeding hairs that cover their tentacles and are their main source of nutrient intake. Being neotenous, swimming clumpstars retain their eyes throughout their lives instead of losing them as abyssal clumpstars do.

Larvae begin life soft and independent, with no shells. They instinctively seek each other out. Once a larva finds a clump or fellow larva, they'll start secreting a communal shell of calcite, which they cling to using cellular baits at the base of their bodies. These communal shells have separate openings for each polyp but merge to comprise a single structure, and if one polyp dies, another may come to occupy its former position. In addition to reproducing by spawning, young swimming clumpstars can fragment, with each one forming a new polyp. If a larva goes too long without finding others of its kind, it will likely fragment and form a clump consisting of clones of itself.