Window-pane Oyster (also known as the Saddle Oyster or Jingle Shell)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Placunidae, Genus: Placuna, Species: Placuna placenta · Placunidae (Window-pane Oyster family) · Bivalve (Clam/Two-shelled); this specimen is a single valve fragment, likely the upper (left) valve, featuring a flattened, irregular disc shape.
Species
Placuna placenta (Most Likely Species - Confidence 85%)
Shell Type
Bivalve (Clam/Two-shelled); this specimen is a single valve fragment, likely the upper (left) valve, featuring a flattened, irregular disc shape.
Family
Placunidae (Window-pane Oyster family)
Size
Approximately 1.5 - 2 cm in length based on the background texture. This is a small juvenile or a fragmentary piece; adults can reach up to 15 cm in diameter.
Color & Pattern
Naturally iridescent and translucent with a pearly, silvery-white to yellowish-grey base. The specimen appears sun-bleached and worn, losing its high-gloss lustre but retaining an opal-like shimmer in certain spots.
Rarity
Common (A very common find in the Moreton Bay/Sandgate area, frequently found washed up among shell grit and seagrass debris).
Habitat
Shallow muddy or sandy bottoms in marine environments, often found in sheltered bays and mangrove-adjacent waters. They are mostly found in intertidal to shallow subtidal zones.
Geographic Range
Indo-West Pacific region, ranging from the Gulf of Aden through Southeast Asia and Northern Australia, including the Brisbane/Moreton Bay area.
Description
A thin, fragile, and remarkably flat bivalve shell. Even as a worn fragment, it displays a distinct nacreous (pearly) texture and a layered, paper-like calcification. The shape is sub-circular but often irregular due to its habit of growing on flat substrates.
Key Features
Extreme thinness, translucency, and a lack of traditional ribs. The presence of a 'V' shaped hinge (if the fragment were larger) and the distinct pearly sheen are diagnostic.
Collector Value
Minimal. While larger, intact specimens are attractive in a collection, small beach fragments like this are considered educational 'beach treasure' rather than high-value collector pieces.
Condition Notes
Poor to Fair. This specimen is a weathered beach-worn fragment with significant erosion on the edges. It lacks the original sharpness of the hinge but retains enough iridescence to identify the family.
Interesting Facts
Historically, these shells were used in the Philippines and India as a substitute for glass in windows due to their translucency—hence the name 'Window-pane Oyster.' The animal within was also once a source of small, low-quality window pearls.
Ecological Role
Suspension feeders that help filter the water column of plankton and organic debris. They provide micro-habitats for small encrusting organisms on their flat surfaces.
Similar Species
Anomia ephippium (Common Jingle Shell) - similar in translucency but usually smaller, more colorful (orange/gold), and more convex in shape.
Beach Finding Tips
In Sandgate and Brighton, look along the high-tide line after a storm. They are often found mixed in with seagrass or buried slightly in the soft mud at low tide near the pier.
Notes
Brighton Sandgate beach Brisbane