There may not be too many fish in the sea, to paraphrase the old song, but there are certainly a lot. Scientists don't have a good idea of just how many fish—or crustacean, sponge, squid, plankton, and even mammal—species there are in the ocean, but they estimate as many as one million. The Census of Marine Life aims to record as much of that as possible by 2010, cleaning up the species registers and expanding them where necessary.

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The first step is making sure there are no duplicates in the catalogue. Experts have so far discovered more than 56,000 species are described more than once. Once they whittled down that list, what remains is now part of the new World Register of Marine Species—the official repository of the census's information.

The bread crumb sponge proved the most egregious offender, garnering a grand total of 56 separate listings, perhaps because it has no fixed address or form and likes to cling to a variety of objects such as floats, pilings or even the undersides of rocks. But it can always be identified by scent: It smells like burnt gunpowder, according to marine biologists.

Even Swedish biologist Carl Linnaeus, modern taxonomy's founder, was not blameless: he gave the sperm whale four different names.

At the same time, more than 1,000 new marine species are discovered every year, including at least 100 fish. The deep sea and Antarctic waters continue to reveal their secrets. For example, recent expeditions to the Weddell Sea between Antarctica and the wider South Atlantic found more than 1,000 new species alone—from single-cell plants to deepwater crabs living miles beneath the ocean's surface.

When the census is complete in 2010 researchers expect to have tallied more than 230,000 individual species for the inaugural effort. But that will not be the end of the work: They estimate that the census will represent a mere third of all the species in the world's oceans. There are still many more fish (species) in the sea. This slide show shows off some of the ones we know.

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