Krocuss are mollusks found in Torvus Bog. They use toxins as nourishment and Krocuss absorb these from gills on their backside. Most weaponry cannot penetrate their hard shell and they can normally only be damaged when their gills are exposed. Samus can also use Power Bombs to destroy Krocuss instantly.
- "The Krocuss thrives on toxins it extracts from its surroundings. It secretes an acidic trail in its wake as it roams in search of nourishment. The durable mollusk can be damaged when it exposes its toxin-absorbing gills: few weapons can penetrate the creature's shell." — Logbook "Krocuss" (Metroid Prime 2: Echoes)