Kleistachi

The Kleistachi has taken to using its four shells for motion. Its major shells are the dorsal and ventral shells, and the minor shells are the two lateral shells. The lateral shells can move forward to seal off the shell and also assist in the Kleistachi's motion. To swim, the Kleistachi can take in water and then forcefully contract its shells to propel itself. Its ventral arms have lost their eyes and are used both for filter-feeding and to help pull the Kleistachi along and bury itself in the substrate when needed.

It is otherwise much like its ancestor. Its shells are made of calcium carbonate, and it reproduces by releasing spore-like gametes into the water. Its young are radial and have a brief free-swimming larval stage which, after developing to their bilateral body forms, will sink to the ocean floor and develop their shells and adult forms.