Lyncina aurantium (Gmelin, 1791)
Golden cowry, 82-105mm

Goldens were unknown at Kwajalein until 1969, when a diver spotted something shiny up in a dark hole in the oceanside slope. A few months later another was found under similar circumstances, but it was another two years before any more were seen. But in the fall of 1971, a “gold rush” started; it seemed that every boat available was carrying divers out to the leeward seaward slope to search for the orange shells. One participant in the rush noted that he’d be rich if he could have sold tickets at Sar Pass, the reef passage leading out to golden country. Although the frenzied searching eventually tapered off, these brilliant orange cowries are still sought by divers, and specimens have been found with some regularity over the past 40 years. Most Lyncina aurantium at Kwajalein Atoll are found on the steep seaward slope on the southern leeward reef, from Kwajalein at the south to Gehh in the north, a span of about 12 miles. A few specimens have been found farther up the leeward reef, along the seaward reef of the northern part of the atoll near Roi-Namur Island, and on the windward reef’s seaward slope near Bigej. Some empty shells have been rarely found on lagoon pinnacles. Depths typically range from 7-25m, although a very few have been found a bit shallower or deeper. Unlike Cypraea tigris, which is about the same size and shares the same reefs, Lyncina aurantium is very intolerant of light. During the day, they live in the darkest holes they can find, as far from light as they can get. Since the reef slope is honeycombed with inaccessible ledges, caves, and deep holes, most specimens of Lyncina aurantium cannot be seen by divers during the day. At night, however, they become active and often can be seen crawling about exposed on the reef or in small ledges feeding on a lumpy gray sponge. This is a Pacific species, ranging from western Polynesia through much of Melanesia and Micronesia westward to the Philippines.

The mantle of the golden is a combination of dark gray with translucent spots and patches that the orange color of the shell shows through. The scattered branching papillae are brownish gray, often white at the bases and tips.

At night they crawl around in ledges and caves, usually with the mantle fully extended. If they keep the mantle fully extended, they blend in quite well. However, they are light sensitive and will often retract the mantle if a diver's flashlight comes close. Then the bright orange shell is easy to see.

This closeup shows the mantle coloration and structure of the papillae.

At night when they move around, they might run into other animals, such as this sleeping parrotfish. It is also a risky time for the shell. We see a fair number of broken up shells, indicating that some shell-crushing predator found one while it was exposed. We have seen large stingrays working along the reef at night; perhaps they are the ones who prey upon hapless cowries.

During the day, the shells hide back in dark holes. The only time you see them in daylight is if one had chosen the wrong hole to crawl into after a night of wandering about, and could not get far enough back in to completely hide.

Juvenile Lyncina aurantium are rarely encountered. This one with its shell still in the very thin bulla stage was one of the few we've seen.

Updated 1 April 2008

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