Saddle Oyster, Nacreous Jingle Shell
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Anomiidae, Genus: Anomia, Species: Anomia trigonopsis · Anomiidae (Jingle shells or Saddle oysters) · Bivalve (Two-shelled); this is a detached upper (left) valve; irregular/sub-circular shape.
Species
Anomia trigonopsis (Confidently identified based on the Brisbane/Sandgate locality and the distinctive internal nacre)
Shell Type
Bivalve (Two-shelled); this is a detached upper (left) valve; irregular/sub-circular shape.
Family
Anomiidae (Jingle shells or Saddle oysters)
Size
Approximately 25-30mm in length. This is a juvenile to mid-sized specimen; adults can reach up to 60mm.
Color & Pattern
Exterior is a weathered chalky grey-white to translucent cream. The interior is characterized by a brilliant 'mother-of-pearl' (nacreous) iridescence with hues of silver, pale green, and pink. No distinct banding is present, but concentric growth lines are visible.
Rarity
Common; frequently found washed up on beaches like Brighton and Sandgate after high tides or storms.
Habitat
Intertidal and shallow subtidal zones. They attach themselves to hard substrates like rocks, larger shells, or jetty pylons using a calcified byssus that passes through a hole in the bottom valve.
Geographic Range
Common along the coastlines of Australia and New Zealand, specifically abundant in the mudflats and rocky shores of Moreton Bay and South East Queensland.
Description
A delicate, translucent bivalve valve with a undulating, irregular margin. The shell is thin and somewhat fragile, possessing a pearly interior luster that resembles an oyster but is much more translucent. The sculpture consists of fine, irregular concentric growth ripples.
Key Features
Highly pearly (nacreous) interior; thin, 'toenail-like' transparency; irregular shape that conforms to the surface it grew upon; lack of a hinge tooth typical of other oysters.
Collector Value
Low monetary value but high aesthetic appeal for beginners. Their value lies in their beautiful luster rather than rarity. Not typically sold in high-end shops but a staple of beachcomber collections.
Condition Notes
Fair to Good. The shell shows significant beach wear and minor erosion on the outer edges. The characteristic internal luster remains intact, though the exterior is somewhat dulled by exposure to sand and surf.
Interesting Facts
Often called 'Jingle Shells' because many of them together in a pocket or jar make a metallic tinkling sound. The animal creates a hole in its bottom valve to reach out and cement itself to a rock, making it immobile for life.
Ecological Role
Filter feeder that helps clear the water of plankton and organic debris. They provide substrate for other small organisms to grow upon and are a food source for crabs and predatory snails.
Similar Species
Placuna placenta (Windowpane Oyster) which is much flatter and larger, or various species of Saccostrea (Rock Oysters) which are much thicker and lack the intense internal translucency.
Beach Finding Tips
Look along the high-tide line (wrack line) among seaweed. They are light and often blow or float further up the beach than heavier shells. Best found at low tide on the muddy-sandy flats of Sandgate.
Notes
Brighton Sandgate beach Brisbane