Atoll
ring-shaped coral reef, generally formed over a former oceanic volcano, frequently with small emerging islands (motus) over the rim, often enclosing a central lagoon possibly still containing one or a few emerging elevated islands
Sabina Shoal
Union banks
Erica Reef
North Danger Reefs
Minerva Reefs
Palmyra Atoll
Johnston Atoll
Ulithi
Pearl and Hermes Atoll
Providence Atoll
Puka-Puka
Howland and Baker islands
Bikini Atoll
Ebon Atoll
Knox Atoll
Hao
Helen Reef
Maria Est
Kiritimati
Swallow Reef
Minto Reef
Lighthouse Reef
Saba Bank
Rocas Atoll
Tarawa
Aldabra
Kwajalein
Funafuti
Glover's Reef
Wake Island
Cocos Lagoon
Scorpion Reef
Rongelap Atoll
Fiery Cross Reef
Ant Atoll
Motu One
Barque Canada Reef
Middleton Reef
Kure Atoll
Arno Atoll
Toke Atoll
Lae Atoll
atoll of the Maldives
Bombay Reef
Makin
Starbuck Island
French Frigate Shoals
Farquhar Atoll