The photocytes of Renilla köllikeri were found to have a diameter of eight to ten micrometers. The mitochondria of the photocytes were found to be very large with abnormally organized cristae surrounding the nucleus of the cell. The rough endoplasmic reticulum of the photocytes were found to exist close to the cell membrane. Several small vesicles, on the order of 0.25 micrometers, were found in the cell, and differently shaped granules containing diverse contents were also observed.