Saddle Oyster (also known as the Jingle Shell and Cap Shell)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Anomiidae, Genus: Anomia, Species: Anomia trigonopsis · Anomiidae (Saddle Oyster or Jingle Shell family) · Bivalve (specifically the upper/left valve); Shape is irregular, sub-circular, and slightly translucent.
Species
Anomia trigonopsis (Common Saddle Oyster)
Shell Type
Bivalve (specifically the upper/left valve); Shape is irregular, sub-circular, and slightly translucent.
Family
Anomiidae (Saddle Oyster or Jingle Shell family)
Size
Approximately 35-45mm in diameter. This specimen is an average adult size; the species typically ranges from 20mm to 75mm.
Color & Pattern
Base color is a creamy yellowish-white with patches of pearly iridescence. Notable dark greyish-black internal scarring and some reddish-purple tinting near the umbo. The interior shows a characteristic nacreous (mother-of-pearl) luster.
Rarity
Very Common. These are frequently washed up on beaches after storms or high tides in Southeast Queensland.
Habitat
Found in intertidal and shallow subtidal zones. They prefer attaching themselves to hard substrates like rocks, other shells (especially dead oyster reefs), or pier pilings using a calcified byssus.
Geographic Range
Common along the coastlines of Australia and New Zealand. Specifically abundant in Moreton Bay, Brisbane, near Brighton Beach and Sandgate.
Description
A thin, fragile, and translucent bivalve valve. The shell is notable for its 'jingle' sound when several are shaken together. It has an irregular, wavy margin and a smooth but undulating surface that often takes the shape of the object it was attached to during life. The interior has a distinct pearly sheen with muscle scar patterns visible as darker blotches.
Key Features
Translucency (light passes through), pearly/silky luster, irregular shape, and the presence of three distinct muscle scars on the interior (though they often merge into a single dark patch in worn specimens).
Collector Value
Minimal monetary value (usually 1.00 USD or less). However, they are highly desired by hobbyists for 'shell art' and jewelry due to their translucency and mother-of-pearl appearance.
Condition Notes
Fair to Good. The shell is a single valve (common for beach finds). It shows some edge wear and minor surface erosion from wave action, typical of beach-collected material from Sandgate. The original nacre is still visible.
Interesting Facts
The common name 'Jingle Shell' comes from the sound they make in beachcombers' pockets. In life, the bottom valve of this shell has a hole (foramen) through which a calcified plug passes to cement the animal permanently to a rock.
Ecological Role
Filter feeder that helps clear the water of plankton and organic detritus. They provide surface area for other small marine organisms to grow upon. Currently not listed as a species of conservation concern.
Similar Species
Monia zelandica (which tends to be larger and more wrinkled) and Placuna placenta (Windowpane Oyster, which is much flatter and used for lampshades).
Beach Finding Tips
Look along the high-tide line at Sandgate after a storm. They are often mixed in with shell grit and seagrass. Because they are so thin, they are easiest to spot when the sun hits the sand, causing their pearly surface to shimmer.
Notes
Brighton beach Sandgate Brisbane