Starcrusher
Splitting off from the Terrorstar is the Starcrusher, an omnivore distinguished by its more advanced and efficient jaw. It has developed additional vertebrae climbing up the back of its head along its nerve chord, with several of these in the head being broad and fitted with the upper jaw to form a skull in adulthood, which helps protect the brain; musculature further connects its lower jaw to the skull such that it has significantly more bite force, no longer being a mere pinch. When biting down hard, its eyes bulge out slightly due to its jaw muscles running under them. The presence of the skull also means it is capable of evolving to have a longer neck as its jaws are no longer attached to its pelvis, though it itself does not do this yet. The embryonic left and right jaw bones, no longer needed to close the jaws, have been repurposed to help control the lateral mandible-spikes instead, allowing it to move them independently of its main jaws. It has developed a tongue-like feature on the inside of its lower jaw, allowing it to chew its food by running this back and forth without having to open its mouth. Rib- and neural spine-like extensions of its vertebrae have developed, especially in its anal arm, helping with strength and stabilization in its limbs.
The Starcrusher has also developed an additional method of obtaining oxygen to supplement its gills—4 primitive lungs, set inside its pelvis, which connect to its 4 nostrils and can be opened and closed. To breathe, it surfaces, flexes to close its gills and open the tube to its lungs, and uses its gills to force air down into them using a similar motion to that which it uses to breathe water. It is still capable of using its gills; however, in addition to granting it more oxygen for an even more active lifestyle, the lungs grant it an additional advantage of better buoyancy, doubling as a sort of swim bladder. It has also advanced its eyes, developing a lens and turning them into a more complex, yet still primitive, camera eye.
With its powerful jaws, the Starcrusher has regained the ability to eat crystal flora and binucleid worms, the latter of which make up a significant portion of its diet, though it continues to take on plenty of other prey as well. It has also developed a raised ridge on its back, which has a similar stabilization purpose to a dorsal fin. Its offspring have also developed more effective jaws; the embryonic jaws fit together decently well, allowing them to take on small soft-bodied prey. Still, the instinct to follow their mothers is retained, and the Starcrusher has begun to intentionally leave behind scraps for following offspring, marking the beginnings of parental care.
The Starcrusher is otherwise much like its ancestor. It mates with any individual it finds using a cloaca at the end of its “anal arm”, its ability to pump its magenta blood is powered by the motion of its fins, and it gives live birth to radially symmetric offspring.