### Identification The Adelaide Top Shell (*Chlorodiloma adelaidae*) is a small but exquisitely sculpted marine gastropod, typically reaching 15–20mm in diameter. Its shell is "turbinate"—shaped like a spinning top—with five to six rounded whorls. The base color is a deep, moody purple-brown or charcoal, overlaid with a striking pattern of cream or pale-yellow zigzagging lines that run axially across the shell.
To distinguish it from the similar *Chlorodiloma odontis* (the Checkered Top Shell), look closely at the aperture (the shell opening). *C. adelaidae* lacks the distinct "toothed" appearance on the columella and instead features a brilliant, iridescent emerald-green or yellow-tinged pearly interior. This shimmering nacre provides a startling contrast to its dark, rugged exterior.
### Habitat & Range This species is a specialist of the southern Australian coastline, ranging from New South Wales through Victoria and South Australia to Western Australia. You’ll find them in the "intertidal theater"—specifically the mid-to-low tide zones of rocky reefs and sheltered bays. They favor crevices, the undersides of boulders, and the roots of seagrass beds (*Posidonia*), where they remain protected from the drying sun and crashing surf.
### Behaviour Observing these snails requires patience; they are slow-motion wanderers. Primarily nocturnal or crepuscular, they emerge as the tide rises to glide across rock surfaces on a broad, muscular foot. When the tide retreats, they retreat into damp fissures, sealing themselves behind a thin, horny "trapdoor" called an operculum to retain moisture. They are solitary but often found in loose aggregations where food is plentiful.
### Diet The Adelaide Top Shell is a dedicated grazer. Using a specialized, ribbon-like tongue called a radula—lined with microscopic, chitinous teeth—it scrapes microfilm, diatoms, and fine macroalgae from the surface of rocks. It acts as a tiny, organic lawnmower, keeping the reef surface clean of overgrowing algae.
### Fascinating Fact The name *Chlorodiloma* literally translates to "Green-Bordered," referring to the stunning neon-green sheen inside the shell’s lip. This "pearly" layer is actually the same material as high-quality pearls (nacre), and if you find a weathered shell on the beach, the dark outer layer often wears away to reveal a completely shimmering, iridescent silver-green orb!