Moonsnail or Moon Shell (specifically the Pear-shaped Moon Snail)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Naticidae, Genus: Mammilla, Species: simiae · Naticidae (Moon Snail family) · Gastropod (univalve); Globular/Spiral shape with a low spire.
Species
Mammilla simiae
Shell Type
Gastropod (univalve); Globular/Spiral shape with a low spire.
Family
Naticidae (Moon Snail family)
Size
Approximately 20-25mm (0.8-1 inch). This is a standard adult size for this species, which generally caps at 30mm.
Color & Pattern
Glossy, creamy-white to light tan base with characteristic wavy or zig-zag reddish-brown axial streaks and bands. The spire is somewhat darker, and the interior (aperture) is typically a smooth, porcelaneous chocolate brown or deep purple-brown.
Rarity
Common; frequently found as empty shells on sandy beaches at low tide.
Habitat
Intertidal and shallow subtidal zones; typically found buried in clean, fine sand or muddy substrates near coral reefs and lagoons.
Geographic Range
Indo-West Pacific region, ranging from East Africa to Polynesia, and very common along the coast of Queensland, Australia (including the Whitsunday Islands/Hayman Island).
Description
A smooth, highly polished globular shell with a short spire and a large body whorl. The surface lacks heavy sculpture, appearing almost glass-like when wet. The most striking feature is the dark, heavy callus that partially covers the umbilicus, and the distinct 'simian' (ape-like) or mottled pattern of brownish streaks on the lighter background.
Key Features
Polished, smooth texture; large, wide aperture; dark brown callus on the inner lip (columella); and the specific wavy brown color pattern which distinguishes it from other plain Naticids.
Collector Value
Low to modest ($2-$10 USD). While aesthetically pleasing and representative of the region, they are quite common. Specimens with exceptionally dark patterns or large size are more desirable.
Condition Notes
The specimen appears to be in Good to Fine condition. The spire is intact and the natural gloss is present, though it shows slight matte weathering typical of beach-found shells. No major chips or predator bore-holes are visible in this view.
Interesting Facts
Moon snails are formidable predators. They use a specialized tongue (radula) to drill perfectly circular holes into the shells of bivalves to consume the animal inside. They also create 'sand collars'—unique egg cases made of sand and mucus that look like discarded plastic or rubber rings.
Ecological Role
Active carnivore and sand-dweller. They help control the populations of bivalves and other gastropods. They are not currently considered threatened or protected in Australia, though live collection in Marine Parks may be restricted.
Similar Species
Mammilla melanostoma (Black-mouthed Moon Snail), which is usually larger and has a more solid dark brown aperture/callus without the wavy exterior streaks.
Beach Finding Tips
Search at very low tide on exposed sand flats or near the edges of seagrass beds. Look for 'plow' trails in the sand where the snail has been burrowing just beneath the surface.
Notes
Australien, Hayman Island