A ring shaped reef composed largely of coral. These features are quite common in the tropical waters of the Pacific Ocean.

A roughly circular reef with an occasional small, low, coral sand island surrounding a shallow lagoon.

1620s, atollon, from Malayam atolu "reef," probably from adal "closing, uniting." Popularized in present form by Darwin's writings.

a coral reef or string of coral islands that surrounds a lagoon. Read more in the NG Education Encyclopedia

a ring-shaped coral reef.

A ring-shaped chain of coral reefs from which a few low islands project above the sea surface. atom

Island surrounded by a coral reef.

An atoll is a ring (or partial ring) of coral that forms an island in an ocean or sea.

ring of coral reefs that surrounds an island that has sunk beneath the waves.

(n) an island consisting of a circular coral reef surrounding a lagoon

(English) A coral reef that circles the mouth of a sunken volcano or lagoon.

An island formed from a coral reef, sometimes circular or horseshoe-shaped, with a lagoon in the center. Atolls usually form around sunken volcanoes.

A horseshoe or circular array of islands, capping a coral reef system perched around an oceanic volcanic seamount

A continuous or broken circle of coral reef and low coral islands surrounding a central lagoon.

A ring-shaped coral reef which has islands or islets on it, the shallow rim enclosing a deeper natural area or lagoon; often springing from oceanic depths.

A horseshoe: shaped or circular reef of coral surrounding a lagoon.

a roughly circular island created by and of coral, most common in the South Pacific, surrounding a lagoon

A coral island consisting of a ring of coral surrounding a central lagoon. Atolls are common in the Indian and Pacific Oceans.

Rear hemisphere heat-seeking missile.

NATO code names for Soviet-manufactured air-to-air missiles.

Russian-built, rear-aspect heat-seeking missile.

A type of island consisting of a ribbon reef that nearly or entirely surrounds a lagoon and supports, in most cases, one to many islets on the reef platform. Atolls have a unique geology, so not all [..]

atoll

A ring shaped coral reef that encircles a lagoon