Gilsto
As a rather bizarre descendant of the Beardgill, the Gilsto has become rather fast, and as a result, has become a fierce predator. Its body has become much more streamlined, which helps to pierce the waters more easily and reach greater speeds, meaning other adaptations had to be made as well. Skin from its head reaches down to form a pouch its tendrils can sit in while not in use, which it uses these for foraging and hunting for benthic organisms. Its lips have decreased in size trememdously, though they have evolved tendril-like extensions from these to make up for that. It mainly uses its lip-tendrils for grabbing and holding onto prey, as well as burrowing. Adults have an interesting behavior, tending to stay in one fixed location, rarely venturing out when either food is scarce or they are looking for a mate. Adults will dig out multiple burrows throughout their life, making and/or moving on from their current burrow when the old one either collapses or is lost. They will mark their current burrow with the stench of their feces, which discourages members of the same species from entering. Juveniles old enough to swim and hunt will not make burrows, but rather bury their entire body in the soil. Gilstos live in both freshwater and saltwater environments. As such, they have salinity-regulating adaptations, most notably a gland that regulates their bodies' salt levels. Its blood adapts from the transition from saltwater and freshwater and vice versa in a similar manner to a bull shark, using specialized kidneys and subtler cell-level adaptations. A crest-shaped structure of cartilage can be found in their fins, which these help them keep shape.
They lay their eggs on various surfaces, such as large rocks, Shrewvs, Nautstars, and many other generally slow-moving organisms that wouldn't try to eat them. When the larvae hatch, their strongest muscles are in their mouth and anal fingers, which they use this to grab onto the nearest surface and filter feed until they are mature enough to swim. Larvae are transparent, which makes it harder to be seen by predators, and they also have simple, fingerless gills instead of their tentacles.
Interactions with Southern Drapiastars
Unlike most other organisms, Southern Drapiastars are one of the harder things to hunt successfully, and they have a surprisingly large amount of ways the two seeing each other could play out. Gilsto will usually try attacking any Southern Drapiastar they see when hunting, and usually go for their backside, though this doesn't work all of the time due to its ring of eyes and extendable mouth. The best time a Gilsto can strike is when it finds a resting individual, though they are harder to spot due to how they're mostly buried, and these attacks normally work about ninety percent of the time. When they are attacked by a Southern Drapiastar in their dens, they will flail violently and try biting them, but if this doesn't work, their last option is to try fleeing.