Fan Shell, Giant Fan Shell, or Razor Clam fragment
Phylum: Mollusca, Class: Bivalvia, Order: Ostreida, Family: Pinnidae, Genus: Pinna or Atrina · Pinnidae (Pen Shell or Fan Shell family) · Bivalve; this specimen is a broken shell fragment representing a portion of one valve, specifically the posterior/mid section.
Species
Likely Pinna bicolor or Atrina pectinata (75% confidence based on hinge and radial ribs)
Shell Type
Bivalve; this specimen is a broken shell fragment representing a portion of one valve, specifically the posterior/mid section.
Family
Pinnidae (Pen Shell or Fan Shell family)
Size
The fragment is approximately 1.5 to 2 inches across. In its complete state, the shell likely reached 10-15 inches in length.
Color & Pattern
Base color is an off-white to creamy beige with hints of translucent amber. There are faint brownish radial streaks and spots. The shell appears weathered and sun-bleached, losing the dark olive-brown periostracum typical of living specimens.
Rarity
Common beach find as fragments; uncommon to find whole and intact due to the shell's extreme brittleness.
Habitat
Inhabits shallow, subtidal mudflats and sandy bottoms. They live partially buried vertically in the substrate, anchored by a strong byssus (silk-like threads).
Geographic Range
Found throughout the Indo-Pacific, including the waters of Queensland, Australia (consistent with Brighton Beach, Sandgate).
Description
This is a weathered fragment of a Pinna shell. It displays characteristic fine, radial ribbing and a thin, translucent, sub-pearly structure. In life, these shells are large, triangular, and fan-shaped, resembling a semi-closed fan or a broad wedge.
Key Features
Thin, brittle, calcitic shell structure; presence of fine radial ribs (costae); triangular growth pattern visible even in fragments; translucent quality when held to light.
Collector Value
Minimal monetary value as a fragment. Whole, large specimens with intact edges can be valued at $10-$40 depending on species and quality.
Condition Notes
Poor condition/fragmentary. It is an eroded piece of a larger shell with significant beach wear, internal pitting (likely from Cliona sponges), and zero hinge or lip integrity. Collectibility grade: Poor.
Interesting Facts
The Pinnidae family is famous for producing 'sea silk' or byssus. Historically, these golden threads were harvested and woven into extremely rare, fine garments for royalty, known as 'cloth of gold.'
Ecological Role
Filters large amounts of seawater; provides habitat for 'pea crabs' (Pinnotheres) which often live commensally inside the shell. Not currently listed as endangered but sensitive to coastal development.
Similar Species
Atrina pectinata (Comb Pen Shell) which has more pronounced prickly scales, or Pinna muricata (Prickly Pen Shell).
Beach Finding Tips
Look in the drift line after a heavy storm or extreme low tide at Sandgate. Search for larger, triangular dark shapes sticking out of the mud; however, be careful as they are very sharp.
Notes
Brighton beach Sandgate