Ultrastructural evidence of the existence of the surface connected canalicular system in the thrombocyte of the shark (Triakis scyllia).

The existence of the surface-connected canalicular system has been demonstrated ultrastructurally in shark [Triakis scyllia) thrombocytes using the ruthenium red method to fix and stain the glycocalyx. In ultrathin sections fixed routinely in glutaraldehyde followed by osmium tetroxide, numbers of electron-lucent vesicles are distributed throughout the cytoplasm. Since ruthenium red-positive reaction product is deposited on the inner surface of these vesicles, they are defined as the surface-connected canalicular system. Moreover, the semithin sectioned thrombocytes fixed by the ruthenium red method provide evidence that the surface-connected system is not composed of vesicles but also of numerous canaliculi. These results suggest that the surface-connected canalicular system is one of the most basic organelles of the thrombocyte system, common to submammalian species and to mammals.