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.
The segmented structure of the sea mouse (Aphrodita aculeata), a kind of polycheate worm, can be seen only if it is turned over because its back is disguised by a thick felt of hairs that mask its segments. Running along each side of its body are numerous stiff, black bristles and a fringe of beautiful, iridescent hairs that glow green, blue, or yellow. The bristles can cause severe irritation if they puncture the skin. The sea mouse is so called because it looks like a bedraggled mouse when washed up dead on the shore.