According to Bunnke (1967), the nervous system of the aelosomatid Aeolosoma consists of a brain, situated dorsally in the prostomium, a periesophageal girdle connecting the brain with the first suboesophageal ganglion, and a ventral nerve cord. We have observed ultrstructural aspects of the Aeolosoma viride nervous system. All the parts of the nervous system are adjacent to the integument cells. In the brain the neurons are found, mostly, dorso-laterally with respect to the nerve fibers (neuropil) and constitute most of the brain. Ultrastructurally, these neurons are diversified by the presence of granulated vesicles of various sizes, respectively 90-120 nanometers (type A) and 60-70 nanometers (type B). Furthermore, type-A neurons have a denser cytoplasm than that of electrons, rich in free ribosomes; conversely, those of type B have a less dense cytoplasm and a smaller number of free ribosomes. Both contain clear not granulated vesicles, of about 40-60 nm in diameter. The nerve fibers of the neuropil have, mostly, a diameter of 0.1-0.5 m and a plasma membrane of about 9 nm and contain granulated vesicles corresponding to those present in the two types of neurons described. Next to these thin fibers, the neuropil contains some thick fibers (0.5-2 m in diameter) and can be regarded as giant fibers (GF). The GF do not have myelin-type sheaths and their plasma membrane (about 9 nm), is separated from that of the thin fibers by a space of about 20 nm. The ganglions of the ventral nerve cord, also placed subepithelially, are formed by a peripheral crown of neurons (about ten) and a central area of fibers. The neurons are of type A and B (the latter slightly predominant) and do not have differentiated characteristics with respect to those described for the brain apart from some lisosomes and/or myelin figures. As for the fibers of the central area their direction is essentially oral-aboral. The GF are visible. The commissures are very reduced. The nerve fibers of the connective tissues, which join ganglions of successive metameres, have a longitudinal direction and have the same type of fibers present in the brain and ventral ganglions. Fibres were found also near the intestine. The structure of the ventral nerve cord looks like that of the polychaetes in the surface position of the ganglions and those of the oligochaetes in the marked shortening of the commissures.

Some ultrastructural aspects on the Aeolosoma viride nervous system

FALCONI, ROSANNA
2009

Abstract

According to Bunnke (1967), the nervous system of the aelosomatid Aeolosoma consists of a brain, situated dorsally in the prostomium, a periesophageal girdle connecting the brain with the first suboesophageal ganglion, and a ventral nerve cord. We have observed ultrstructural aspects of the Aeolosoma viride nervous system. All the parts of the nervous system are adjacent to the integument cells. In the brain the neurons are found, mostly, dorso-laterally with respect to the nerve fibers (neuropil) and constitute most of the brain. Ultrastructurally, these neurons are diversified by the presence of granulated vesicles of various sizes, respectively 90-120 nanometers (type A) and 60-70 nanometers (type B). Furthermore, type-A neurons have a denser cytoplasm than that of electrons, rich in free ribosomes; conversely, those of type B have a less dense cytoplasm and a smaller number of free ribosomes. Both contain clear not granulated vesicles, of about 40-60 nm in diameter. The nerve fibers of the neuropil have, mostly, a diameter of 0.1-0.5 m and a plasma membrane of about 9 nm and contain granulated vesicles corresponding to those present in the two types of neurons described. Next to these thin fibers, the neuropil contains some thick fibers (0.5-2 m in diameter) and can be regarded as giant fibers (GF). The GF do not have myelin-type sheaths and their plasma membrane (about 9 nm), is separated from that of the thin fibers by a space of about 20 nm. The ganglions of the ventral nerve cord, also placed subepithelially, are formed by a peripheral crown of neurons (about ten) and a central area of fibers. The neurons are of type A and B (the latter slightly predominant) and do not have differentiated characteristics with respect to those described for the brain apart from some lisosomes and/or myelin figures. As for the fibers of the central area their direction is essentially oral-aboral. The GF are visible. The commissures are very reduced. The nerve fibers of the connective tissues, which join ganglions of successive metameres, have a longitudinal direction and have the same type of fibers present in the brain and ventral ganglions. Fibres were found also near the intestine. The structure of the ventral nerve cord looks like that of the polychaetes in the surface position of the ganglions and those of the oligochaetes in the marked shortening of the commissures.
ISAO 2009
56
56
R. Falconi
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/86560
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