Saddle Oyster (also known as Jingle Shell or Mermaid's Toenail)
Phylum: Mollusca, Class: Bivalvia, Order: Pectinida, Family: Anomiidae, Genus: Anomia, Species: Anomia trigonopsis · Anomiidae (Jingle Shell or Saddle Oyster family) · Bivalve (specifically a single upper/left valve), irregularly disc-shaped or rounded.
Species
Anomia trigonopsis (95% confidence based on Brisbane location and morphology)
Shell Type
Bivalve (specifically a single upper/left valve), irregularly disc-shaped or rounded.
Family
Anomiidae (Jingle Shell or Saddle Oyster family)
Size
Approximately 30-40mm in length. This is a medium-sized specimen for this species, which can reach up to 60-70mm in Australian waters.
Color & Pattern
The interior shows a vibrant, pearly nacre with strong silver, pink, and green iridescence. The exterior appears to be a dull, chalky grey-white, which is typical for beach-worn specimens. The color is natural but shows some weathering.
Rarity
Very Common. These are frequently found washed up on sandy beaches after high tides or storms in the Brisbane area.
Habitat
Found in intertidal and shallow subtidal zones. They prefer to attach themselves to hard substrates like rocks, jetty pylons, or other shells using a calcified byssus that passes through a hole in the lower valve.
Geographic Range
Common across Australia, particularly along the eastern and southern coastlines, including the Moreton Bay region (Brighton and Sandgate beaches).
Description
An irregularly shaped, translucent bivalve with a distinctively pearly interior. The shell is thin and somewhat fragile, often conforming to the shape of the object it was originally attached to. The interior nacre has a metallic sheen that catches the light beautifully, while the outer surface is rough and lamellose (layered).
Key Features
Distinguished by the intense pearlescent interior, the absence of a visible hinge teeth structure, and the characteristic muscle scar pattern. The thin, 'glassy' texture of the shell material is diagnostic for the Anomiidae family.
Collector Value
Low monetary value ($1-$5) due to their abundance, but high aesthetic value for crafts, jewelry, and beginner collections. Specimen valuation increases for pairs (both valves) or shells with rare natural yellow or orange tints.
Condition Notes
Fair to Good. This is a beach-worn upper valve. It lacks the lower valve (which usually has the hole). There is some minor chipping around the margins and typical surface erosion, but the interior nacre remains highly reflective. Collectibility grade: Good.
Interesting Facts
The common name 'Jingle Shell' comes from the sound multiple shells make when shaken together or used in wind chimes. Unlike most oysters, they are more closely related to scallops. The animal produces a unique calcified 'plug' to anchor itself permanently to a spot.
Ecological Role
They are filter feeders that help clarify the water by consuming phytoplankton. They provide habitat for tiny encrusting organisms and serve as a food source for predatory gastropods and sea stars.
Similar Species
Monia zelandica (which tends to be larger and more wrinkled) and Placuna placenta (Windowpane Oyster, which is much flatter and more circular).
Beach Finding Tips
Look along the high-tide line (the wrack line) at Brighton or Sandgate beaches. They are easiest to spot on sunny days when the wet nacre reflects the light. They often hide among clusters of broken shell grit and seaweed.
Notes
Inside of shell from Brighton & Sandgate beach in Brisbane