Morphology, structure and innervation of the statocyst in Octopus variabilis

Abstract:

The morphology and innervation of the statocyst in Octopus variabilis are examined by using light microscope, scanning electron microscope(SEM), transmission electron microscope(TEM) and Synchrotron radiation. The result reveals that the statocyst tissues are paired membrane sacs suspended in cartilage cavities by surface fibers, and located respectively beneath the eyes in back of head. There are two sensory epithelia in each statocyst: the macula and the crista. A single calcium statolith is covered by a mucus layer and is only lying over the top of macula hair cells. The tips of kinocilia of the macula hair cells that protrude into the crevices among loosely arranged crystal units of the ventral bottom layer of the statolith mass. Hair cells in crista are arranged in a spiral shaped strip. It consists of nine sections and all are covered by copular. Scanning electron microscope (SEM) examinations indicate that there are only equal lengths long kinocilia in hair cells surrounded by short length of microvillia, but no stereocilia are found in statocyst. The transmission electron micrographs (TEM) confirm that the kinocilia are in 9+2 tubular structure. Our Synchrotron radiation examination results reveal that there is only one ramus of nerve from brain to innervate the macula system while there are two separated nerve rami to the crista that are branched again to innervate different target sections of the hair cell strip respectively.