Vellicator
The vellicator split from the devorator before it transitioned into the mailclad devorator, diverging by combining a new feeding strategy with a drastic reduction in size.
Like the devorator, the vellicator can only eat food a fair bit smaller than itself, but their new strategy revolves around ripping off soft bits of their prey and swallowing those chunks. Their tentacles now have barbs that they use to tear off their food. When not in use, the tentacles lock together into a tapered mouth shape, the barbs fitting against tough chitinous plates. There's no ability to chew; they swallow the chunks whole.
This feeding strategy has been especially useful against the midnight and twilight gills, as it allows vellicators to nip at the gills and other exposed spots, especially in the relatively undefended midnight gills. It even lets them nibble goliath shevs a little bit, by grabbing any partially exposed pseudopods they can.
Vellicator behavior has changed too. Individuals aren't much smarter, but rather than mate or fight with their fellows, they can now swarm together when bringing down larger prey, though this is liable to result in fights over food afterwards. This slight increase in sociality has rendered asexual reproduction unnecessary; they now only reproduce by sexual spawning.
Like its close relative, the mailclad devorator, the vellicator has become more streamlined than the ancestral devorator, though this may be by convergence. It too has adopted a lunate tail for efficiency in nonstop swimming. The vellicator retains the three rings of chitin, but they are flush with the skin rather than protruding outwards, so the streamlining is maintained. Each ring of chitin now sports paired fins and a dorsal fin, though the ones in front are still the largest. These replace other protrusions from the rings but using the fin-formation genes. The vellicator's eyes have lost their distinctive chitinous iris in favor of a pupil which is able to dilate and contract. The vellicator has a long torpedo-like shape.
The vellicator stores oxygen in its hemerythrin-using blood, to use when plunging into the oxygen-poor abyssal depths or for sudden bursts of speed. Otherwise, its internal systems are little changed from the ancestral devorator, with gills that require constant movement, a large chitin-plated stomach, and three notochords. The sensory equipment is much the same as well, with UV bulbs and UV-sensitive eyes with a chitinous sclera. They've expanded the electroreceptor ampullae in the mouth-tentacles for greater sensitivity for their hunting.