Hairy Mussel (or Bearded Mussel)
Phylum: Mollusca, Class: Bivalvia, Order: Mytilida, Family: Mytilidae, Genus: Trichomya, Species: Trichomya hirsuta · Mytilidae (True Mussel family) · Bivalve (specifically a single valve of a two-shelled mollusk); fan-shaped to wedge-shaped.
Species
Trichomya hirsuta
Shell Type
Bivalve (specifically a single valve of a two-shelled mollusk); fan-shaped to wedge-shaped.
Family
Mytilidae (True Mussel family)
Size
Approximately 25-30mm in length. This is an average juvenile to mid-sized specimen, as adults typically reach 40-60mm.
Color & Pattern
Dark chocolate brown to blackish exterior with a slightly iridescent, pearly purple or white interior. The most striking feature is the golden-brown, hair-like periostracum (outer protein layer) that covers the ribs.
Rarity
Common. They are frequently found washed up on beaches in Queensland, especially after storms or high tides.
Habitat
Found in the intertidal and shallow subtidal zones. They prefer attaching to rocks, other shells, or jetty pylons in sheltered bays and estuaries using strong byssal threads.
Geographic Range
Endemic to Oceania; predominantly found around the coasts of Australia (from Queensland down to Tasmania and South Australia) and New Zealand. Collecting location (Brighton/Sandgate) is a classic habitat for this species.
Description
A distinctive bivalve characterized by its 'bearded' appearance. The shell is subtriangular or wedge-shaped with prominent radial ribs. These ribs are covered by a thick, bristly periostracum that forms long, stiff hairs, particularly toward the posterior margin. The shell is sturdy and slightly inflated.
Key Features
The presence of coarse, stiff hairs (bristles) on the outer shell; fine radial ribbing beneath the hairs; terminal umbones (beaks situated at the very end of the shell).
Collector Value
Minimal monetary value ($1-$5) due to high local abundance, but high educational/interest value for those interested in specialized marine adaptations. Collectors prize specimens with a full, undamaged 'beard'.
Condition Notes
Good. The specimen retains much of its diagnostic periostracum (the 'hair'), which often wears off in beach-worn shells. The hinge area appears slightly eroded, but the valve is intact.
Interesting Facts
The 'hairs' are actually part of the shell's outer skin and are thought to help camouflage the mussel from predators or prevent the settlement of other encrusting organisms. They use a 'byssus' (a bundle of silk-like threads) to tether themselves so tightly to rocks that they can withstand heavy surf.
Ecological Role
Filter feeder that helps clear the water column of organic particles. They provide habitat for tiny crevices-dwelling invertebrates within their colonies and serve as a food source for oyster catchers and predatory sea snails.
Similar Species
Modiolus barbatus (Bearded Mussel of the northern hemisphere) and Septifer bilocularis. Trichomya hirsuta is distinguished by its specific ribbing pattern and the stiffness of its bristles.
Beach Finding Tips
Look among shell grit and drift lines near rocky outcrops or mangroves. At Sandgate/Brighton, they are most common after a stiff onshore breeze has dislodged them from nearby subtidal reefs.
Notes
Brighton beach Sandgate