For such tiny animals, Syllidae really get around.
These polychaete worms, most only a few millimeters long, are found from the intertidal to the deep sea. The over 200 species of Syllids, and potentially many more not yet recognized, are keeping some molecular biologists very busy. 133 species from 5 continents have DNA barcodes already, and our colleagues at the Moorea Biocode project just keep finding more, just waiting to be identified, or classified as new species.
(via: Encyclopedia of Life)
Nereis cf riisei, rolled in a spiral
Photo by Arthur Anker: http://www.flickr.com/photos/artour_a/284887021/in/set-72157623477677107
Portrait of a hesionid worm, Moorea
Photo by Arthur Anker: http://www.flickr.com/photos/artour_a/2954331656/in/set-72157623477677107