Cryptophyte algae are robbed of their organelles by the marine ciliate Mesodinium rubrum

Mesodinium rubrum (Lohmann 1908) Jankowski 1976 (= Myrionecta rubra ) 1 , 2 is a common photosynthetic marine planktonic ciliate which can form coastal red-tides 3 . It may represent a ‘species complex’ 4 , 5 and since Darwin's voyage on the Beagle , it has been of great cytological, physiological and evolutionary interest 4 . It is considered to be functionally a phytoplankter because it was thought to have lost the capacity to feed and possesses a highly modified algal endosymbiont 5 , 6 . Whether M. rubrum is the result of a permanent endosymbiosis or a transient association between a ciliate and an alga is controversial 7 . We conducted ‘feeding’ experiments to determine how exposure to a cryptophyte alga affects M. rubrum . Here we show that although M. rubrum lacks a cytostome (oral cavity) 8 , it ingests cryptophytes and steals their organelles, and may not maintain a permanent endosymbiont. M. rubrum does not fall into recognized cellular or functional categories, but may be a chimaera partially supported by organelle robbery.