Oxyrrhis marina cells coexist with bacteria, probably in some type of symbiotic relationship. The figure shows O. marina cells from antibiotic-treated cultures in close relationships with unidentified bacteria. A, B: Scanning electron micrographs showing the oral region of O. marina with rod-shaped bacteria attached. C: Fluorescence in-situ hybridization of an O. marina cell using a fluorescent probe that recognizes a conserved region of bacterial small subunit (16S) ribosomal RNA genes following the standard protocol described in http://www.arb-silva.de/fish-probes/fish-protocols/. Blue: DAPI-stained nucleus of O. marina; red dots: bacteria.