ISSN:
0362-2525
Keywords:
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Medicine
Notes:
Electron microscope studies on Tylocephalum metacestodes embedded in the tissues of the oyster, Crassostrea virginica, have revealed that the tegument of the larval tapeworm is comprised of an external and an internal level which are partially separated by a basal lamina and two layers of muscles. The outer tegumentary level is comprised of an anucleate, cytoplasmic syncytium in which are embedded large and small vesicles and mitochondria. Surfacial hooks are also embedded therein. The internal level is comprised of relatively large discrete cells including mitochondria, rough endoplasmic reticulum, and large and small vesicles. These cells are intermittently connected with the external level by cytoplasmic bridges.Arising from the external level are unusual microvilli each of which terminates as a spherical vesicle. The stem of each microvillus is covered by a unit membrane which is continuous with that overlaying the body surface. In addition, each microvillus includes an external layer of medium electron density, a medial layer of intense electron density, and a core of heterogenous, medium electron density. These structures may be intertwined and bundles can be observed at the light microscope level as fibril-like projections from the parasite's body surface. One of their possible functions may be to prevent intimate contact between the encapsulating fibers of host origin and the parasite's body surface. In addition, the contraction and distention of the circular muscles result in microvillar movement which may keep the surrounding host fluids, including those of nutritional importance to the parasite, in a state of flux thus hypothetically permitting more uniform uptake.The abundance of vesicles in the syncytial external level of the tegument appears to be characteristic of the more primitive marine cestodes belonging to the orders Trypanorhyncha and Lecanicephala.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jmor.1051300104
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