Varying Estimates
The number of marine species is uncertain. The World Register of Marine Species lists about 245,000 described species, with estimates of total diversity ranging from 500,000 to over 1 million. The Census of Marine Life suggested up to 10 million species, while broader extrapolations range from 2 million to 100 million.
Many undiscovered species are likely small or microscopic, and ongoing research continues to reveal marine biodiversity.