Carvebull
The carvebull is a large relative of the beastbull that migrated back up to the twilight zone in search of food. It now heavily specializes in large invertebrate prey.
Carvebulls are much more agile than their slow-moving ancestors, and have some subtle but important modifications to their fins in order to suit their lifestyle. The lateral fins have more flexible joints, allowing them to easily lay flat on the side of the organism, reducing drag. They are also smaller and more streamlined. Their thicker, more powerful tail fin gives them great boosts of speed, allowing them to effectively ambush their large, slow-moving prey. Their dorsal fin has enlarged, and a slight ridge on their tail has elongated into a smaller, posterior version of the dorsal fin.
As this species’ ancestors went upwards, they found a bounty of large prey to eat. In order to deal with the tough exoskeletons of their prey, they have adapted multiple styles of feeding. These creatures are able to smell food from quite far away, and use that as their primary method of finding their prey. Once they are close enough to a prey item, they quickly bolt towards it using their powerful tail fin. Depending on the size of their prey, they may do one of two things. If the prey is small enough, they simply grab and crush it from wherever it gets a hold of its prey. This works well for the twilight neodevorator and the twilight euryptile, which usually don’t get much bigger than the carvebull. For large prey, though, they have a different method. Carvebulls get their name from how they deal with giant filter feeders such as the filter chad. They first hook onto the organism with their six serrated “teeth”, which are derived from their ancestral lateral jaws. In order to help slice into prey, they have also developed a tough keratinous beak. This helps a lot with the filterclad and filter lad, who do not have much exposed flesh. However, this beak does help a lot more with the filter chad, whose large amount of exposed skin makes them easier to bite into. Once they have established a firm grip, they will thrash around side to side until they rip off a chunk of flesh. Most of this carving is done with the bottom jaw, as it has the teeth-like lateral mandibles fused to it. This isn’t good for any organism, but the filter chad survives this far more often than its smaller relatives do.
Otherwise, its reproduction, skeletal structure, and general morphology hasn't changed too much from its ancestor. However, on the path that it is headed, it may become even more stealthy and streamlined than it already is. Only time will tell.