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A World Apart

By Kennedy Warne
8/16/2014 9:14:18 AM

The following text and image are an excerpt from the September issue of National Geographic magazine:

"The most common species, Tridacna maxima, is better known by a name that seems to contradict itself: the "small giant clam." These mollusks are a little longer than an American football, but they are dwarfed by individuals from the largest clam species,Tridacna gigas, which can exceed four feet in length. At first glance the small giants look like they're wearing blue, indigo, green, or another shade of lipstick. In fact the color comes from pigment cells inside their fleshy mantles, which protrude like wavy lips when the shells are open.

An underwater paradise in the remote Pacific Ocean that includes the sea around Caroline Island, seen here, will be protected-thanks in part to National Geographic's Pristine Seas project. © Brian Skerry/National Geographic

The giant filter-feeders act as water purifiers. Microbiologists on the expedition measured bacterial concentrations at every atoll they visited and found Millennium's clam-filled lagoon to have the lowest count. Bacteria can cause diseases in coral, fish, shellfish, and crustaceans such as crabs. Low concentrations in seawater are an indication of a healthy marine ecosystem."

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