Not all the continents are large landmasses. A few are submerged, including the Kerguelen Plateau and Zealandia.
The Kerguelen Plateau is in the southern Indian Ocean, 3,000 km southwest of Australia, about 3 times the size of Japan: extending for more than 2,200 km. The plateau was born from a hotspot that arose when Gondwana broke up 130 MYA. Some small islands sit above sea level.
New Zealand and New Caledonia are the lovely landmasses representing Zealandia, a largely (93%) submerged continental fragment that sank after breaking away from Australia 60–85 MYA, after a previous separation from Antarctica 85–130 MYA. 3.5 million km2, Zealandia is nearly half the size of Australia.
The Sunda Shelf extends from the continental shelf of Southeast Asia into the Gulf of Thailand to the Sunda Islands, notably Sumatra and Borneo.
During glacial periods, including the Last Glacial Maximum (26.5–19.5 thousands of years ago (TYA)), sea level dropped, exposing vast expanses as marshy plains. Sea level was at a minimum 22 TYA. Humans lived on the Sunda Shelf then.
In the post-glacial period, sea level rose; at first slowly, then moderately, peaking with a rapid rise of 16 meters in the 300 years between 14.6–14.3 TYA
On juicy rumor, Greek philosopher Plato wrote in 360 BCE that the legendary island of Atlantis was a conquering naval power ~9,600 BCE. According to Plato’s myth, after failing to invade Athens, Atlantis sank into the sea “in a single day and night of misfortune.” If there are grains of history in the legend of Atlantis, they rose and sank with Sundaland.