Violet Knightworm
The violet knightworm originated as a population of beach knightworms moved south into temperate and polar regions. Already adapted to eat Photosagnia rombusi, they found new abundant photosagnians across the beach zones, which they came to specialize in. This also prevented them from migrating further northwest, for the West Darwin Temperate Beach lacked photosagnian food.
They've taken on an increasingly terrestrial lifestyle and no longer rely on colony crystals to build nests. Instead, the violet knightworm males dig nests in the ground, slightly above the spring tide line, and emit pheromones to attract mates. On arrival, the females lay semi-soft eggs into the nests, which the male then fertilizes before the eggs harden. They then bury the eggs and leave. Once the young hatch, they dig themselves out. They build similar burrows to hibernate during the winter. Interestingly, the violet knightworm's active lifespan is similar across their range, but they hibernate for much longer near the pole than in the temperate zone, so in temperate areas they only live for a few years total, but near the pole, they may live for more than a decade in total.
They no longer rely on the colony crystal to maintain their shell, either. The shell grows rather slower and bunches up in the jagged spikes on the back, but they will also subdue its growth by rubbing it on hard surfaces in their environment, mostly stones and crystal flora.
The overall body plan is similar to before. They have a soft core containing their organ systems and a hard outer shell consisting of four segments. Their tracheae are versatile enough that they can breathe air as well as water, though they breathe more efficiently when they are moist, so they still spend plenty of time immersed. They have adopted a violet color to blend with their preferred food. They have less need for their antennae, which have atrophied slightly.