AbstractCells of euglenoidTrachelomonasEhrenb. vary in the size, shape and appearance of the external envelope’s ornamentation, as well as internal structure. The loricae are generally similar in color, ranging from light (hyaline, yellowish, golden, reddish, brownish) to dark (brown, black). This study examined the loricae of twelve trachelomonad species, some light (yellow to golden) and some dark (brown). There were no black loricae, suggesting that little or no Mn was taken up by the cells. Though the envelopes differed in surface ornamentation and color, comparative SEM-EDS analyses of all the material studied showed high iron content, silicon mineralization, and no manganese. The degree of iron and silicon mineralization varied. Some loricae had high silicon content (e.g.,T. compactaMiddelhoeck) and others were more saturated by iron ions (T. manginiiDeflandre,T. lacustrisDrezep.).