The chunky knightworm replaces the greater knightworm in its environment. It is similar to its ancestor, but larger, and also a lot bulkier—a feature which allows it to have larger guts better suited for digesting large amounts of flora; melter detritis exist in its gut, which are necessary for breaking down the crystal bits it consumes and which also take off some of the energy load of digestion overall. Its radula tongue is elongated and much stronger, allowing it to scrape away at tougher foods, including the crystalline parts of crystal flora. Its legs have gained an additional segment, increasing the efficiency of its locomotion, and its third pair of legs has been further modified into a pair of paddles to help it swim rather than only being able to crawl. Its cloacal legs have fused into a single gonopodium on the back of its last body segment, which makes mating easier; when mating, the male inserts the tip of his into a larger opening slightly lower on the female's, and since there is only one on each individual and there are fewer moving parts there is less risk of slipping midway through the process. This change also makes mating with related species more difficult, which protects them from wasting energy on unfit hybrid offspring
Unlike its ancestor, the chunky knightworm’s dorsal spines are greatly exaggerated. This is because the size of them is an indicator of eating well, so those with larger spines have better reproductive success. Its last body segment has also gained a crystal-like appearance and luster, which similarly indicates good health. After mating, it lays thousands of eggs which are dispersed by water; the great number is because most of the offspring are eaten by various filter-feeders.