Chromodoris reticulata, a species of sea slug which is found in the Pacific Ocean, is able to detach, re-grow and then re-use its penis.
(They are not the only creatures known to lose their male organs after sex; orb weaving spiders do it, as does a sea creature called the periwinkle and land slugs belonging to the genus Ariolimax. However the researchers believe that Chromodoris reticulata is the first creature known that can re-grow its appendage, and it is this ability that has surprised scientists. Surprised! There's an understatement.)
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