Windowpane Oyster (also known as the Capiz shell or Saddle Oyster)
Kingdom: Animalia; Phylum: Mollusca; Class: Bivalvia; Order: Ostreida; Family: Placunidae; Genus: Placuna; Species: Placuna placenta · Placunidae (Windowpane Oyster family) · Bivalve (Right valve); translucent, flattened, and roughly circular/disc-shaped.
Species
Placuna placenta (Confidence level: High)
Shell Type
Bivalve (Right valve); translucent, flattened, and roughly circular/disc-shaped.
Family
Placunidae (Windowpane Oyster family)
Size
Approximately 7-9 cm wide. Adults can reach up to 15 cm in diameter.
Color & Pattern
Naturally translucent with a pearly, silvery-white or off-white base. This specimen shows significant environmental staining, including yellow-brown oxidation and dark grey/black mineral deposits, likely from resting in silty or anaerobic mud at Brighton Beach.
Rarity
Common (found regularly on beaches in Queensland, especially after storms or high tides).
Habitat
Shallow, muddy or silty bays and estuaries. Found in the intertidal and subtidal zones, usually lying flat on the seabed in soft sediment.
Geographic Range
Indo-West Pacific region, ranging from the Gulf of Aden to the Philippines and throughout Northern and Eastern Australia, including Moreton Bay/Brighton Beach.
Description
A flat, paper-thin bivalve known for its remarkable translucency. The shells are extremely compressed, almost resembling a piece of mica or frosted glass. The surface is relatively smooth with faint concentric growth lines. In its live state, it is nearly clear enough to read through.
Key Features
Total flatness of the valves; extreme translucency; 'V' shaped internal hinge ligament (though restricted to the interior); brittle, flaky texture characteristic of calcite and aragonite layers.
Collector Value
Low commercial value in this stained 'beach-find' condition ($1-$3). High educational value as a local representative of the family. Clean, white commercial specimens are sold in bulk globally.
Condition Notes
Fair condition for a beach-worn specimen. The shell shows chipping along the fragile margins and significant surface discoloration from Moreton Bay's silty substrate. It lacks the 'Gem' quality of commercially harvested specimens used for decor.
Interesting Facts
Historically, these shells were cut into small squares and used as window glass in Spanish colonial churches in the Philippines (Capiz windows). They are also the source of 'Capiz' items found in home decor. Unlike true oysters, they do not attach to rocks.
Ecological Role
Suspension feeders that filter plankton from the water column. They are an important prey source for rays and certain species of sea stars and gastropods. They help improve water clarity in muddy estuarine environments.
Similar Species
Anomia ephippium (Jingle Shells), which are usually smaller, more colorful, and have a distinct hole in the lower valve for a byssus attachment.
Beach Finding Tips
In Brighton/Sandgate area, look for these during low tide on the muddy flats or along the high-tide drift line after a windy day. They often blend in with the sand when wet due to their translucency.
Notes
Brighton beach Brisbane