Pacific Jewel Box (also known as the Leafy Jewel Box or Clear Jewel Box)
Phylum: Mollusca, Class: Bivalvia, Order: Venerida, Family: Chamidae, Genus: Chama, Species: Chama arcana · Chamidae (Jewel Box family) · Bivalve (Fragment of an upper valve). This is a fan-shaped/irregularly circular valve fragment.
Species
Chama arcana (High confidence based on location and rib structure)
Shell Type
Bivalve (Fragment of an upper valve). This is a fan-shaped/irregularly circular valve fragment.
Family
Chamidae (Jewel Box family)
Size
Approximately 0.75 to 1 inch in diameter. This is a small juvenile specimen or a worn fragment; adults typically reach 1.5 to 3 inches.
Color & Pattern
The exterior is creamy white to Tan with distinctive reddish-brown to orange-brown radial stripes/streaks following the ridges. The interior appears a dull pearly white. Colors are slightly faded due to beach wear.
Rarity
Common (The species is abundant, but finding perfectly intact 'leafy' specimens is uncommon as the spines break easily in the surf).
Habitat
Intertidal and shallow subtidal zones (up to 50 meters deep). These are sessile organisms that cement their lower valve to rocks, shipwrecks, or other shells.
Geographic Range
Eastern Pacific, specifically from Oregon, USA, down to Baja California, Mexico. Very common in Southern California waters like Coronado.
Description
A robust, thick-walled bivalve fragment known for its 'leafy' appearance. This specimen shows several strong radial ribs. In life, these ribs would support delicate, translucent scale-like spines. The texture is rough and calcified, characteristic of shells that must withstand heavy wave action.
Key Features
Deep radial ridges, reddish-brown color streaks concentrated on the ribs, and an irregular, almost 'crumpled' growth habit. The inner margin often has fine crenulations (teeth).
Collector Value
Low ($1-$5). While beautiful when intact with full spines, beach-worn fragments are primarily of interest to hobbyist beachcombers rather than high-end malacological collectors.
Condition Notes
Fair. This is a beach-worn upper valve. The delicate 'leafy' scales/spines have been eroded away by sand and surf. There is no hinge ligament present. It is a 'beach find' quality specimen rather than a 'gem' specimen.
Interesting Facts
Jewel Boxes are called 'sessile' because they are permanently attached to a substrate. They are often overgrown with sponges or algae, making them look like part of the rock until they open their valves to filter feed.
Ecological Role
Filter feeders that help clear the water column of organic particles. They provide habitat for secondary occupants like small crabs or worms that hide among their spines.
Similar Species
Chama pellucida (Translucent Jewel Box) which has more translucent scales, and Pseudochama exogyra (Reversed Jewel Box) which attaches by the opposite valve.
Beach Finding Tips
Look in the 'wrack line' or amongst shell hash near rocky jetties or tide pools after a high tide or storm. Their weight often causes them to settle in depressions in the sand.
Notes
Coronado beach