PZ Myers has just posted a detailed writeup of some new evo-devo work looking at the evolutionary relationship between ascidians (sea squirts), cephalochordates (Amphioxus), and vertebrates. Sea squirts and cephalochordates always confuse my students, as they're in the same phylum as us (Chordata), yet they're not vertebrates (i.e., they don't have a skull or backbone). Sea squirts are particularly cool, as they're sessile filter feeders, and thus look nothing like vertebrates.
PZ reports that the evolutionary relationship of these three groups is being revised: those wacky sea squirts are now thought to be evolutionarily closer to us than cephalochordates are. PZ does more than just say that, though: he also goes into lots detail about the developmental biology of ascidians1. It's all good, so go read the post already.
1 Be sure to look for the figure showing that some ascidians develop adult characteristics well before they metamorphose!