Ultrastructure of bacterial symbiont within dinospore of Hematodinium sp. from Crangon crangon . (A) bacteria-like symbionts generally occupied electron lucent vacuoles within the spore cytoplasm of the majority of individual parasites observed (white arrow). Empty electron lucent vacuoles (asterisk) and mitochondria (black arrows) were seen in close proximity to endosymbionts. (B) Single bacteria-like symbiont within the nucleoplasm of the parasite (as shown in Figure 3C). Note the apparent absence of the electron lucent vacuole generally seen surrounding bacteria-like symbionts occupying the cytoplasm. (C) Dividing endosymbiont within the cytoplasm of the parasite cell. Note in this case, the endosymbiont was not surrounded by a vacuolar membrane buy instead lay in direct contact with the host cytoplasm, albeit surrounded by an electron lucent halo (arrow).