Chama (The Jewel Box Clam)

The bivalve (clam) genus Chama Linnaeus, 1758 belongs to family Chamidae Lamarck, 1809. The geologic record of the genus is Paleocene to Recent. Extant (living) species are found mostly in shallow-tropical waters (intertidal to 100 m depth). There are a few species, however, that live in cool waters (e.g., in Oregon and California). The common name of this bivalve is the “Jewel Box.” 

Chama is a small to medium-size heterodont bivalve, which means it has only a few teeth, and they are subdued and somewhat degenerate. This is because Chama normally cements itself to the substrate (e.g., in crevices within coral-reef rock), therefore, large teeth are not needed.

Chama lazarus Linnaeus, 1758 is a moderately common species of Chama found in water depths ranging from 1 to 20 m, in the Indo-Pacific region. The specimen shown below is from the Philipine Islands.

This first image shows both valves closed together (articulated). The shell is 75 mm height (including projections of the spines) and 55 mm width (including projections of the spines). The right valve is on the left side of this image. During life, the right valve would be facing upward, so as to discourage a predator from biting down on the sharp spines. 

This second image shows the exterior of the right valve, whose sharp bladed spines are encrusted by some patches of calcareous red algae, small worm tubes, and bryozoan colonies (nearly microscopic).

This third image shows the exterior of the left valve, which is attached to a piece of colonial coral. The left valve, which is the "lower" valve, also has some bladed spines, but they are absent where the valve makes contact with the substrate. Thus, this bivalve always has its sharp spines present on any vulnerable part of its shell.

This last image shows the interiors of both of the valves (left valve on the left and right valve on the right). The brown material just above the teeth is the thin ligament, which helps hold the valves together.