HAD TO LINK TO THIS

Fishes of the Gulf of Maine. What a fantastic site. Check out Paralichthys dentatus, vs. Pseudopleuronectes americanus , for example. On one of those science trips in Long Island Sound (can't remember where from: Mystic? New London?) the guide told us that these two fish actually are only distantly related: they didn't evolve from a common ancestor -- with one branch "leaning left" and one "leaning right," for example -- but are actually from different ancestors, with the end result being species that are, in one sense, mirror opposites. Here's one; for the other, you'll have to visit the site.

The above image of the Summer Flounder is from this page:

http://octopus.gma.org/fogm/Paralichthys_dentatus.htm

From the online edition of "Fishes of the Gulf of Maine," by Henry Bigelow and William C. Schroeder, FISHERY BULLETIN 74, FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE, Volume 53 [Contribution No. 592, Woods Hole Oceanographic Institution], UNITED STATES GOVERNMENT PRINTING OFFICE - Washington: 1953, (Revision 1.1: 2002)