Hundreds of new species of invertebrates have been discovered in the Wedell Sea of Antarctica. Three German expeditions from 2002 to 2005, trawling at depths between 1,000 and 6,000 meters, found the marine life to be far richer than anyone expected. There are nearly 600 new species from just one group, the isopods (which resemble marine woodlice).
Accompanying the article above in The Economist is an editorial discussing just how complex this whole business of describing species really is. Whether a scientists uses morphology, reproductive isolation (aka the Biological Species Concept or BSC) or DNA, classifying and bounding a species remains a fuzzy business.