Jingle Shell, Saddle Oyster, Mermaid's Toenail
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Anomiidae, Genus: Anomia, Species: Anomia trigonopsis · Anomiidae (Jingle shells/Saddle oysters) · Bivalve (single upper valve shown); Sub-circular, irregular disc shape
Species
Anomia trigonopsis (Common Saddle Oyster)
Shell Type
Bivalve (single upper valve shown); Sub-circular, irregular disc shape
Family
Anomiidae (Jingle shells/Saddle oysters)
Size
Approximately 25-35mm (1-1.4 inches) in diameter. This is a mid-sized specimen; the species can reach up to 60-70mm.
Color & Pattern
Translucent chalky white to pearly silver with a notable slate-gray/purplish smudge near the umbo (hinge area). Features concentric growth rings and a subtle nacreous (pearly) luster. The shell appears slightly weathered and sun-bleached, typical of beach-cast specimens.
Rarity
Very Common
Habitat
Found in intertidal and shallow subtidal marine environments. They typically attach themselves via a calcified byssus to rocks, other shells (especially oysters), or pier pilings.
Geographic Range
Indo-Pacific region, very common along the Australian coastline, specifically the Eastern seaboard near Brisbane (Moreton Bay area), New Zealand, and surrounding waters.
Description
A thin, translucent, and somewhat fragile bivalve valve. The shell is characterized by its irregular shape which often conforms to the substrate it was attached to. The exterior shows concentric lamellae (growth lines). The most striking feature of Anomiidae is the interior pearly luster which persists even after the animal has died.
Key Features
Single translucent valve; irregular 'potato chip' thinness; diagnostic dark muscle scar/stain near the hinge; pearly interior luster; lack of prominent radial ribs compared to scallops.
Collector Value
Minimal monetary value ($1-$2 USD), but high aesthetic value for crafts, wind chimes, and jewelry. It is a staple for coastal beachcombers in Queensland.
Condition Notes
Fair to Good. This is a beach-worn upper valve. It lacks the bottom valve (which usually has a hole for the byssal attachment). The margins are slightly eroded, and the natural translucency is somewhat dulled by exposure to sand and sun.
Interesting Facts
The name 'Jingle Shell' comes from the sound many of them make when shaken together in a bag or a jar. In life, the bottom valve has a hole in it through which a calcified 'plug' or foot extends to cement the shell permanently to a hard surface. They are often called 'Mermaid's Toenails' due to their translucent, curved appearance.
Ecological Role
Filter feeder that helps clarify coastal waters by consuming plankton and suspended organic matter. They provide micro-habitats for smaller encrusting organisms on their upper valves.
Similar Species
Monia zelandica (larger, often more green/yellow) and Placuna placenta (Windowpane Oyster, which is much larger, flatter, and more circular).
Beach Finding Tips
Look along the high-tide line at Sandgate after a storm or strong easterly winds. They are often found mixed in with shell grit and debris. Search for the distinctive pearly flash amongst the duller cockle and whelk fragments.
Notes
Brighton Sandgate beach Brisbane