Nautcracker
The Nautcracker split from its ancestor. It has gained a taste for hard-shelled fauna such as Nautstars and Dappershells, using its powerful beak to crack their shells open. In order to accomplish this, its keratin features--its teeth and beak--are now so calcified that they are better described as being formed from calcium carbonate with keratin for support than the other way around, greatly increasing their strength. Despite the high calcification, the beak is stained a darker color to keep it from standing out. The beak has also gained an especially heavily mineralized, almost enamel-like edge for extra strength. Its face is short and its beak occupies most of it. Its tusks are now inside the beak, though they have been reduced and act more like the rest of the teeth. The extra dorsal fin on the anal arm of its ancestor has flattened back into a more useful keel.
The anatomy of the Nautcracker’s gills has changed. To streamline the flow of water, the gills open out only on the inner side. The gills move in and out to pump water through them, as in other vertebrate asterzoans, and due to the change they can actually do this more effectively. As such, the gills are highly mobile to the point that they can be used as fins--a truly bizarre accidental side effect of their increased efficiency. Though this was certainly not the intended purpose, it nonetheless greatly impacted how their shape evolved. Its flippers are smaller as a result, its gills starting to replace their purpose. The gills are supported by strips of cartilage radiating like fin rays.
The Nautcracker gives birth to even more developed offspring than its ancestor. Newborn Nautcrackers almost resemble miniature adults, though with a nub of what was once the raptorial arm still visible before it’s absorbed. Baby Nautcrackers still follow their parents, but gain independence and start hunting small shelled fauna fairly quickly once their beaks have fully hardened. The Nautcracker mates by “holding hands”, pulling back the small membrane stretching between the anal fingers making up the tail fin to help it hold onto a mate and perform a cloacal kiss.