Ultrastructural Observation of Pseudoamphisiella lacazei Reveals More Morphological Features and Provides Taxonomical Evidence

Ultrastructure of Pseudoamphisiella lacazei was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with an improved sample preparation method. The major results included: 1) A vacuole layer which had been considered absent in this species was found, which indicated that the cortex layers should thus contained three layers: a smooth membrane, a vacuole layer, and a fiber layer. 2) Extrusomes were found to distribute among the cortex vacuoles, and they were supposed to be a type of mucocyst which were similar to the mucocyst of Urostylida based on their shape and structure. 3) Some bacteria were observed to be attached to the fiber layer as if they were endosymbionts of P. lacazei. In order to analyze the features and taxonomical position of Pseudoamphisiella, morphological features of all four species of Pseudoamphisiella were compiled and compared. Our results suggested that ultrastructure observation could supplement and correct the gross and micro-level observation and provide additional evidence to the taxonomical argument