Sea cucumbers
Sea cucumbers are the only echinoderms that demonstrate "functional" bilateral symmetry as adults, as they lie horizontally as opposed to the vertical axis of other echinoderms.
Source
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"Conspicuous Sea Cucumber, Coconut Island, Hawaii."
http://en.wikipedia.org/wiki/File:Conspicuous_Sea_Cucumber,_Coconut_Island,_Hawaii.JPG
Wikipedia
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