Rainbowtesta
When cupotestas floated south into the northern temperate Vailnoff Ocean, they found an area almost barren of food. The best available food source was rainbowhedrons, whose outer shells were tougher to digest than their former diet of mainly adorbalgae. But they adapted.
Like its ancestor, the rainbowtesta consists largely of a cup-shaped body around a large stomach, which contains ribbon-tailed detriti to aid in digestion. The body contains a series of air pockets, connected to the stomach, used to suck food in, adjust buoyancy, and expel waste, water, and offspring. This system has expanded to include several digestive pouches, which provide concentrations of enzymes and ribbon-tailed detriti for the longer process of breaking down rainbowhedrons. They also can ingest sand to help grind down the shells. This sand also serves as ballast, which combines with their air pockets to give them much finer control over their depth. This expansion means that their body extends further below their stomach than before, though it remains quite soft.
They've expanded further south throughout the Vailnoff Ocean, where they can supplement their diet with other food, like various photosagnians and krakowhexians, but they continue to specialize in rainbowhedrons. Juvenile rooted leafstars also exist throughout their range but are bigger than their usual fare. The rainbowtesta will most likely be able to digest just a little from it before it gets out.
Sexual selection has also played a role in rainbowtesta's evolution. They preferred mates with the most colorful bioluminescent displays, and there were no predators to restrain them. The bioluminescent spots are much smaller, so each row has many more of them, and they now have four rows instead of two. These shift through a panoply of colors, a bright and dazzling array.
Furthermore, this attraction to color results in a preference for rainbowtestas with a variety of rainbowhedrons in their stomach. Rainbowhedrons come in a wide array of colors too, mostly varying by depth, and rainbowtestas are translucent enough that it's possible to glimpse some of the colors of their partially-digested food. So this further encourages rainbowtestas to take on a wide vertical range.
As before, they exhibit trilateral symmetry. There is a ring of three pairs of simple fins near their base, which can also expand and shrink hydrostatically. Above is a row of three pairs of hectocotyli: sperm-transferring tentacles. These shrink and fold to the side when not in use (left or right depends on the individual). In use, they expand hydrostatically, filled with fluid, which allows them to clasp another rainbowtesta's hectocotyli. Small reproductive organs above the hectocotyli produce sperm and eggs. The hectocotyli transfer sperm from outward-facing pores by the reproductive organs before mating, and transfer received sperm into the same openings afterwards. The reproductive organs store received sperm and over time release them bit-by-bit to fertilize their eggs. They expel their young through the same pores soon after fertilization.
The hectocotyli are useful for gathering sand too. They'll stir up sand on the ocean floor and transfer it into their bodies much the same way as they receive sand, but instead of sticking in the reproductive organs, they transfer the sand through the series of air and digestive pockets to get to where its needed. Rainbowtestas can also clasp each other for non-mating purposes to form chains when they're in areas of particularly abundant food.
They also have six compound eyes in two rings, between each pair of hectocotyli and fins. These consist of many more facets than the cupotesta had, which are arranged in a more coherent cup shape, but they do not have any kind of lens. They are optimized for detecting colors, not for resolving images. Each eye facet detects a different hue, allowing the eyes as a whole to serve almost like a spectroscope. This is very useful for spotting mates and different varieties of rainbowhedrons. By noting which eyes see which colors, they can get a vague idea of direction, but nothing more distinct than that. Each eye has a cluster of nerves behind it, but they have also developed a simple brain in the expanded base of the body to coordinate their behavior. Their range of behaviors is very simple, largely related to migrating between ocean surface and floor, selecting mates, finding food, and collecting sand.