Observations on an unusual membrane complex found in gregarines parasitic in the barnacle Balanus tintinnabulum

Abstract

The surface of gregarine trophozoites consists of a three-layered membrane complex thrown into a series of lamellae. The complex is composed of an outer plasmalemma, subjacent pentalaminar layer, and underlying homogeneous, electron dense layer. The pentalaminar layer is 140–170 Å thick and exhibits a morphology reminiscent of fused, cell membranes seen in tight junctions, myelin figures, and nerve myelin. The pentalaminar layer is derived from subsurface cisternae found in sporozoites. The underlying homogeneous, electron dense layer is 450–500 Å thick. Pores and caveolae are found as specializations of the pentalaminar and homogeneous electron dense layers. Dense vesicles, similar in morphology to the pentalaminar caveolae, are found in the peripheral cytoplasm. Endoplasmic reticulum is closely associated with the caveolae and the dense vesicles. The location of the membrane complex at the surface and the presence of pores and caveolae in its structure suggests some transport and/or segregation function.