Small Giant Clam (also known as Crocus Clam or Boring Giant Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Subfamily: Tridacninae, Genus: Tridacna, Species: T. crocea · Cardiidae (Cockle and Giant Clam family); formerly Tridacnidae · Bivalve (two-shelled); this is a single valve (half-shell). It features a fan-shaped, corrugated profile.
Species
Tridacna crocea (Confidence Level: 90%)
Shell Type
Bivalve (two-shelled); this is a single valve (half-shell). It features a fan-shaped, corrugated profile.
Family
Cardiidae (Cockle and Giant Clam family); formerly Tridacnidae
Size
Estimated at 4-5 inches (10-12 cm). This is adult size for Tridacna crocea, which is the smallest of the giant clam species, rarely exceeding 6 inches.
Color & Pattern
Exterior is grayish-white with hints of creamy yellow and tan. It shows distinct wavy patterns and concentric growth rings. The interior (though not fully visible) appears to be a glossy, porcellaneous white. The colors appear naturally weathered and somewhat sun-bleached.
Rarity
Common in its natural geographic range, but Uncommon to Rare as a pristine beach find due to its habit of being embedded in coral. It is highly regulated in international trade.
Habitat
Found in shallow marine waters, typically 0–20 meters deep. They are unique for boring into coral limestone or reef substrates until only the top edge of the shell is visible.
Geographic Range
Indo-West Pacific region, ranging from the South China Sea and Japan to Australia (Great Barrier Reef) and across to Fiji.
Description
A heavy, thick-walled bivalve characterized by 4 to 5 deep, fold-like radial ribs. The shell surface is sculpted with concentric lines and low scales (scutes), which are often worn smooth in this species compared to others in the genus. The shell is strongly inequilateral with a large opening (byssal foramen) near the hinge for the animal to attach to rocks.
Key Features
Boldly undulating margins that interlock with the opposing valve; deep radial folds; specialized large byssal opening; relatively smooth scutes compared to T. maxima.
Collector Value
Low to Moderate ($10–$30) for a single valve in this condition. Specimens are more valuable when paired (both valves) and in 'Gem' condition. Highly regulated under CITES Appendix II, making legal international transport difficult without permits.
Condition Notes
Fair to Good. The shell shows significant erosion, likely from being tumbled in the surf or being extracted from coral. The 'teeth' of the margin are slightly worn, and the scutes are mostly eroded. It lacks the luster of a 'Gem' specimen but serves as a fine anatomical example.
Interesting Facts
Tridacna clams are 'photosynthetic' animals; they host symbiotic algae called zooxanthellae in their colorful mantle tissue, which provides them with nutrients from sunlight. Unlike the related T. gigas, which can reach 4 feet, T. crocea remains small enough to be popular in the home aquarium trade.
Ecological Role
Functions as a reef-builder and water filterer. These clams are currently listed as 'Least Concern' on the IUCN Red List, but are vulnerable to over-harvesting for the aquarium trade and food, as well as habitat loss from coral bleaching.
Similar Species
Tridacna maxima (Small Giant Clam) which has a more elongated shape and more prominent scales/scutes, and Hippopus hippopus (Horse's Hoof Clam) which has reddish blotches and no large byssal opening.
Beach Finding Tips
Look in reef rubble zones or near-shore coral lagoons during low tide in the Indo-Pacific. They are rarely 'washed up' whole because they attach so firmly to the reef; usually, only old, dead valves are found loose.
Notes
Pass