Opabinia. Found in the Burgess Shale in British Columbia Canada. It's not an arthropod. How can it even be a bilateria? With five eyes? It's still unassigned to any group. No one knows. A transitional species?
Source: http://www.nmnh.si.edu/paleo/shale/popabin.htm
http://evolution.berkeley.edu/evolibrary/article/0_0_0/cambrian_06
Has to be related to Anamalocaris?:
Source: http://www.learningfamily.net/reiser/9809-nathisttour/0_cambrian.htm
See also:http://dml.cmnh.org/2001Mar/msg00025.html
http://omniknow.com/common/wiki.php?in=en&term=Opabinia
Source: http://www.nmnh.si.edu/paleo/shale/popabin.htm
http://evolution.berkeley.edu/evolibrary/article/0_0_0/cambrian_06
Has to be related to Anamalocaris?:
Source: http://www.learningfamily.net/reiser/9809-nathisttour/0_cambrian.htm
See also:http://dml.cmnh.org/2001Mar/msg00025.html
http://omniknow.com/common/wiki.php?in=en&term=Opabinia