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1

Ultrastructure of the infective eggs of the hymenolepidid cestode, Ditestolepis tripartita [Zarnowski, 1955], a parasite of shrews

100%
Swiderski Z., Tkach V.
Acta Parasitologica
|
1997
|
tom 42
|
nr 1
The ultrastructure of infective eggs of the hymenolepidid cestode, Ditestolepis tripartita, a parasite of shrews, was examined with emphasis on cellular organisation of mature oncospheres. Each hexacanth larva is surrounded by three main egg envelopes: thin layer of amorphous outer envelope, relatively thick layer of inner envelope with an embryophore and a delicate oncospheral membrane. The outer and inner envelopes of infective eggs of D. tripartita are usually amorphous; the embryophore is relatively thin and moderately electron-dense. Five major types of oncospheral cells have been distinguished. These consist of: (1) about ten germinative cells; (2) about 30 somatic cells (= myocytons of somatic and hook muscles); (3) a bi-nucleate medullary centre (= tegumental perikaryon); (4) a bi-nucleate, U-shaped penetration gland and (5) two cells of neurosecretory type with characteristic dense-cored vesicles. The hook-muscle system with complex interconnections between different muscle fibers provides a structural basis for coordinated hook action.
2

Differentiation and ultrastructure of the oncospheral envelopes in the hymenolepidid cestode Staphylocystoides stefanskii [Zarnowski, 1954]

100%
Tkach V. V., Swiderski Z.
Acta Parasitologica
|
1998
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tom 43
|
nr 4
Ultrastructure of the oncospheral envelopes in developing and fully formed eggs of the hymenolepidid cestode, Staphylocystoides stefanskii (Zarnowski, 1954), is described. The uterus in this species is saccular, with deep infoldings of the uterine wall which form pocket-like structures. The uterine wall is composed by a flat syncytial uterine epithelium containing elongated nuclei with prominent nucleoli. The differentiating and mature oncospheres are surrounded by three envelopes: (1) an outer envelope; (2) an inner envelope consisting of three layers - an extraembryophoral cytoplasmic layer, a dense and relatively thick embryophore, and an intraembryophoral cytoplasmic layer; (3) a thin oncospheral membrane, surrounding the oncosphere. The outer envelope usually contains 2 nuclei in the preoncospheral stage, however, no nuclei were observed in this layer in the fully formed eggs. The inner envelope shows in sectioned material 1-2 nuclei in its intraembryophoral layer. The extraembryophoral layer of the inner envelope increases in thickness during the egg maturation. The embryophore was initially discontinuous, formed by the blocks of the electron-dense substance, and situated directly under the outer limiting membrane of the inner envelope. Later the neighbouring blocks fuse together and finally produce a continuous dense layer of embryophore. The embryophore remains slightly vacuolised for some time and finally forms a thick homogeneously electron-dense layer. The oncospheral membrane appears striated on the high-power micrographs. The ultrastructure of oncospheral envelopes in S. stefanskii is compared with those in other mammalian hymenolepidids.
3

Electron microscopical studies on the cellular organisation of the oncospheres of the hymenolepidid cestode, Staphylocystoides stefanskii [Zarnowski, 1954]

88%
Swiderski Z., Tkach V. V.
Acta Parasitologica
|
1999
|
tom 44
|
nr 1
The cellular organisation of the oncospheres of S. stefanskii has been examined by means of light and transmission electron microscopy. The reconstruction of hexacanth larvae was based on serial semithin sections and its results have been correlated with partial reconstruction from ultrathin sections. The surface of the oncospheres was covered by a thin layer of oncospheral tegument. Five major cell types have been distinguished in mature oncospheres of S. stefanskii: (1) about 10 germinative cells, situated in the posterior pole of the oncosphere; (2) about 36 somatic cells (= myocytons of somatic and hook muscles); (3) a bi-nucleate medullary centre representing a perikaryon of oncospheral tegument; (4) a bi-nucleate, U-shaped penetration gland and (5) two nerve cells containing characteristic dense-core vesicles. The total number of cells in mature oncospheres was thus about 50, while the number of nuclei was about 52. The hook-muscle system of oncospheres, composed of peripheral and hook muscles, is similar to that described in other cyclophyllideans. The oncospheral hooks were formed in specialised hook-forming cells or oncoblasts. The oncoblasts are retained in mature oncospheres only as a thin layer of anucleated cytoplasm around the hook handle region, which seems to be a common feature for the mammalian hymenolepidids. The data on the oncospheral cell types and their number are in agreement with formerly proposed hypothesis (Swiderski 1972, 1983), assuming that the progressive reduction in number of oncospheral cells is one of the characteristic features in cestode evolution.
4

Ultrastructural studies on the cellular organisation of the oncospheres of the nematotaeniid cestode, Nematotaenia dispar [Goeze, 1782]

88%
Swiderski Z., Tkach V. V.
Acta Parasitologica
|
1997
|
tom 42
|
nr 3
A complete reconstruction of the constituents of the mature egg of N. dispar has been attempted at the light microscope level based on serial semithin sections, and results have been correlated with partial reconstruction from ultrathin sections. The outer coat of the oncosphere consists of an anucleate cytoplasmic layer of tegument, a basal lamina, and two layers of peripheral, somatic musculature. The oncospheral hooks and their associated muscle system, situated in the anterior pole of the larvae, together with penetration gland secretion appear to play an important role in host tissue penetration. The bases of each lateral hook pair are joined by a common zone of “connective” material whereas the medial hook bases are embedded in individual cups of this material. Five major types of oncospheral cells have been distinguished. These consisted of: (1) a bi-nucleate medullary centre (= subtegumental cell); (2) a bi-nucleate, U-shaped penetration gland; (3) two nerve cells of neurosecretory type; (4) about 34 somatic cells (= cell bodies of somatic and hook muscles); and (5) about 12 germinative cells, arranged in two groups of six cells, situated in the posterior pole of the hexacanth. The position of oncospheral structures remains fixed in relation to one another but at the same time is somewhat arbitrary due to the high plasticity of the hexacanth during movements.
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