Vinagoblet
This offshoot of the vinagob spread into shallower waters. As larvae, they are nearly indistinguishable from their ancestor (though smaller): cup-like organisms with a big stomach that dissolves the small organisms it eats, with two rings of four fins each, a dangling tail, and air pockets for sucking in food and adjusting buoyancy, and rings of bioluminescence.
As adults, however, they settle in the sand of the sea floor. The tail burrows down and holds the vinagoblet in place. The lower four fins extend downward and turn into hooks, which hold the vinagoblet steady. They aim for somewhere shallow but outside the tidal zone, as their stomach is vulnerable to drying out when exposed to air.
The vinagoblet continues to filter-feed much as before. They retain the system of air pockets, now distributed more widely through the body, but the pockets become filled with a series of adjustable fluids, as they no longer have access to surface air. These can suck water into the stomach, thereby taking in small organisms that will slowly be digested by a pool of enzymes and symbiotic ribbon-tailed detriti.
They've further honed their digestive system, as well. Thin digestive hairs (which develop early in the larval stage, one of the main ways to distinguish vinagoblet larvae from vinagobs) line the ribbed stomach, allowing direct absorption of nutrients from the stomach. Similar digestive hairs also grow along the upper fins (again, starting as larvae), thus letting the vinagoblet filter-feed across a more substantial area. These fin-hairs can only absorb particularly small microorganisms.
The sedentary lifestyle does present a challenge in the form of settling sand and debris. As a result, the vinagoblet developed an expanded system of expulsion vents. Although they retain expulsion vents that face outward, allowing a steady stream of water into the stomach and out the sides, these cannot point downward (or they risk uprooting themselves). They now grow addition expulsion vents that point back into the stomach, connected through interlocking pockets, alternating with the intake vents. This allows them to expel water back into the stomach, thus cleaning out accumulated debris. They can also set up a directional flow, so that water comes in one side of the stomach and out another, periodically changing.
Vinagoblets constantly produce sperm and eggs within specialized reproductive organs above each former fin. These sperm are immediately ejected through the outward-facing vents, and swim off to seek another vinagoblet. The eggs remain in sacs within the body, and may be fertilized by newly arriving sperm. Fertilized or not, they will develop into a vinagoblet larva, expelled in turn through the same vents.