Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images of the activation and the attachment step of the infection process of Pasteuria ramosa in Daphnia magna. (a) SEM image of a resting stage of P. ramosa. (b) TEM image of resting stage before activation. The exosporium (ex) encloses the two peripheral fibres (pf) and the endospore (en). (c) SEM image of activated spores trapped by Daphnia phyllopods. (d) TEM image of activated spores in Daphnia oesophagus. Top left: the spore is in the process of activating and shedding the exosporium. Bottom right: the activated spore with its sombrero-like structure in cross-section. Spore coat (sc) surrounding the cortex (cx). (e) TEM image of peripheral fibres (pf) and its microfibres on the upper side (upf) and on the lower side (lpf). The upper side is more furnished in microfibres and is more likely to play a role in the attachment. (f) TEM image of Pasteuria attached to the Daphnia oesophagus wall (ew). The nomenclature were defined according to the nomenclature of Pasteuria penetrans in .