A University of Auckland scientist working on a worldwide project to count all the creatures in the sea, believes that more than half of all marine species may still be undiscovered.
In the study, The Magnitude of Global Marine Species Diversity, researchers calculated that there are fewer than 1 million life forms in the sea, a lower total than previously thought.
According to Auckland University's Dr Mark Costello, around 226,000 species have been discovered by science, and as many as 72,000 more are in collections awaiting description.
Most of the undiscovered species lurk in remote, deep parts of the ocean, and are typically forms of smaller crustaceans, molluscs, algae, worms and sponges.
Scientists said that the study shows that the rate of discovery is increasing, with an unprecedented 20,000 new marine species described in the last decade alone, suggesting that most marine species will be discovered this century.
"This is by far the most comprehensive assessment of how many marine species have been described to date, and how many described species experts believe there may be.
"Knowing how many species there are in our oceans, and describing them, is vital for science and conservation for several reasons," said Costello.
He said the research provided a measure of tracking progress of the species, and enables more accurate estimates of potential species extinction rates.
It is the culmination of fourteen years' work for Costello, who began a European Register of Marine Species in 1997 that expanded until the World Register was initiated in 2006.
The World Register of Marine Species - an open-access, online database that has received contributions from almost 300 scientists from 32 countries - set the stage for the current research.