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Ultrastructure of intrauterine eggs: Evidence of early ovoviviparity in the caryophyllidean cestode Wenyonia virilis Woodland, 1923

100%

Mlocicki D., Swiderski Z., Mackiewicz J. S., Ibraheem M. H.

Acta Parasitologica

2010

tom 55

nr 4

349-358

Ultrastructural evidence for early intraurerine embryonic development of Wenyonia virilis is presented. At the initial stage of egg formation, the fertilized oocyte or ovum is surrounded by numerous vitellocytes and newly formed eggshell. Individual vitellocytes undergo progressive fusion into a vitelline syncytium. During cleavage divisions, three types of blastomeres are formed: macromeres, mesomeres and micromeres. Two large macromeres contain a large nucleus with spherical nucleolus and numerous small heterochromatin islands dispersed in moderately electron-dense nucleoplasm. The granular cytoplasm shows a few large mitochondria. Medium-sized mesomeres contain a spherical nucleus with numerous heterochromatin islands, adjacent to the nuclear envelope, and a prominent electron-dense nucleolus. Their nuclei are embedded in granular cytoplasm with a few large and numerous small mitochondria and Golgi complexes. The small micromeres are characterized by presence of spherical nucleoli with large areas of highly condensed heterochromatin and a few islands of granular electron-lucent nucleoplasm. Their granular cytoplasm shows a few small lipid droplets and several spherical mitochondria. Majority of micromeres give rise to the hexacanth but many of them also undergo degeneration or apoptosis. Both mesomeres and macromeres are engaged in the formation of the oncospheral envelopes. The outer envelope is formed by a fusion of two macromeres whereas the inner envelope originates from a fusion of mesomeres. The intrauterine eggs of W. virilis usually contain an embryo at the early preoncopheral phase of development and possesses three primary envelopes: (1) thick eggshell; (2) thin cytoplasmic layer of the outer envelope and (3) inner envelope. Based on embryonic development, egg type and life-cycle characteristics, caryophyllideans tend to show closer affinities to spathebothriideans than to the former pseudophyllideans.

Ultrastructure of oncospheral envelopes and their differentiation in the cestode, Dicranotaenia coronula [Dujardin, 1845] [Cyclophyllidea, Hymenolepididae]

100%

Chomicz L., Swiderski Z., Grytner-Ziecina B.

Acta Parasitologica

1995

tom 40

nr 1

Studies of the ultrastructure of oncospheral envelopes and their differentiation in the hymenolepidid cestode Dicranotaenia coronula in utero revealed four main envelopes: (1) capsule, (2) outer envelope, (3) inner envelope with a thin, electron-dense embryophore, and (4) oncospheral membrane. An additional hemispherical calotte, the hook region membrane covers one pole of the oncosphere and is attached to its surface. Both the outer and inner envelope represent syncytial layers which contain large, flattened nuclei of blastomeres which participated in their formation: nuclei of macromeres in the outer, and nuclei of mesomeres in the inner envelope. The granular cytoplasm of the both envelopes contains a large amount of free ribosomes, numerous mitochondria and several lipid droplets. The primary inner envelope of the early embryo forms in the later stage of embryogenesis its two derivatives: the embryophore and the oncospheral membrane. The hook region membrane oryginates from a syncytial binucleate complex by delamination of its cytoplasmic plate. Both the ultrastructural features of oncospheral envelopes and mode of their differentiation are compared with those described previously in the other hymenolepidids with aquatic and terrestrial life cycles. The ultrastructure of the oncospheral envelopes in D. coronula is discussed in relation to its life cycle and to environmental conditions in which the infective eggs remain for a certain period of time, until eaten by benthal ostracods, the intermediate hosts of D. coronula.

Ograniczanie wyników

2 Acta Parasitologica

2 Swiderski Z.

1 Chomicz L.

1 Grytner-Ziecina B.

1 Ibraheem M. H.

1 Mackiewicz J. S.

1 Mlocicki D.

1 2010

1 1995

Wyniki wyszukiwania

Ultrastructure of intrauterine eggs: Evidence of early ovoviviparity in the caryophyllidean cestode Wenyonia virilis Woodland, 1923

Ultrastructure of oncospheral envelopes and their differentiation in the cestode, Dicranotaenia coronula [Dujardin, 1845] [Cyclophyllidea, Hymenolepididae]