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1

Ultrastructure of the intrauterine eggs of Didymobothrium rudolphii [Monticelli, 1890] [Cestoda, Spathebothriidea, Acrobothriidae] and its phylogenetic implications

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Swiderski Z., Gibson D. I., Santos M. J., Poddubnaya L. G.
Acta Parasitologica
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2010
|
tom 55
|
nr 3
254-269
The intrauterine polylecithal eggs of the spathebothriidean cestode Didymobothrium rudolphii (Monticelli, 1890) were examined by means of transmission electron microscopy (TEM). Each unembryonated egg is composed of a fertilised oocyte or ovum and several vitelline cells, all surrounded by a newly formed shell. The lumen of the proximal uterus is packed with unutilised vitelline material and eggs at different stages of shell formation. In the proximal region of the uterus, the fertilised oocytes, initially surrounded by dense, discontinuous islands of eggshell material and containing long axonemes of spermatozoa in their cytoplasm, were frequently observed. Sperm axonemes also remain in the oocyte cytoplasm of eggs surrounded by a thick electron-dense shell until the sperm nucleus is transformed into a male pronucleus. Despite the fact that the two-pronuclei stage and cell divisions within the eggs of D. rudolphii were never observed, individual eggs containing several blastomeres of different sizes were seen in the middle and distal regions of the uterus. This provides indirect evidence that at least a few initial cleavage divisions must take place in the intrauterine eggs and direct evidence that the early embryonic development of D. rudolphii starts in utero. The several vitellocytes present in each egg contain nutritive reserves for the developing embryos; these are composed mainly of numerous lipid droplets and a moderate amount of glycogen. In the eggs containing early embryos composed of several blastomeres, the cytoplasm of the degenerating vitellocytes exhibits the presence of so-called ‘foci of cytoplasmic degradation’, which appear to be involved in the autolytic process of the vitellocyte cell components and inclusions, such as a high accumulation of lipids and glycogen. This progressive degeneration of the vitellocytes, considered as an example of programmed cell death or apoptosis, likely contributes towards the resorption of nutritive reserves by the developing embryo. Some of the results of this study are commented upon in relation to the affiliation of the spathebothriideans with other lower cestode groups.
2

Fine structure of egg-forming complex ducts, eggshell formation and supporting neuronal plexus in progenetic Diplocotyle olrikii [Cestoda, Spathebothriidea]

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Poddubnaya L. G., Mackiewicz J. S., Swiderski Z., Brunanska M., Scholz T.
Acta Parasitologica
|
2005
|
tom 50
|
nr 4
Ultrastructural descriptions of the oviduct, fertilization canal, seminal receptacle, ovovitelline duct, vitelline reservoir, ootype, Mehlis' gland, proximal uterus, and neurosecretory elements associated with egg-forming ducts are given for the progenetic spathebothriidean tapeworm, Diplocotyle olrikii from the body cavity of Gammarus oceanicus. The functional significance of cortical granules of the oocyte, as necessary elements for joining vitelline material to an oocyte in the ovovitelline duct, is established. The proximal ootype has a vesicular epithelium and is the site of initial, nascent eggshell formation. Precursors of nascent eggshell are vesicles, synthesized in both the proximal ootype wall and vitelline cytoplasm that become associated with the newly formed shell. Major shell structure comes from subsequent deposition of shell globules from a disintegration of vitelline clusters. Mehlis' gland has a single secretory cell type. Secretory granules from Mehlis' gland become associated with the developing egg that passes through to the distal ootype and proximal uterus where egg-formation is completed. It is not known, however, whether Mehlis' gland secretion promotes breakdown of free vitelline cells, liberation of shell globules, confluence of shell globules on the developing eggshell or provides further structural components for the shell. Despite some differences in ootype morphology, the basic process of eggshell formation in D. olrikii may share much in common with the Pseudophyllidea and Caryophyllidea. Small vesicles and dense-core vesicles are in nerve terminals near duct musculature. Nerve terminals with large dense vesicles are described near, in, and within the seminal receptacle, fertilization canal and distal ootype. The possible physiological effects of exocrine neurosecretions are discussed.
3

Ultrastructural studies on the reproductive system of progenetic Diplocotyle olrikii [Cestoda, Spathebothriidea]: Ovarian tissue

100%
Poddubnaya L. G., Mackiewicz J. S., Brunanska M., Scholz T.
Acta Parasitologica
|
2005
|
tom 50
|
nr 3
The ultrastructure of the ovary and oogenesis are described from the immature and sexually mature female reproductive system of the progenetic spathebothriidean tapeworm, Diplocotyle olrikii from the body cavity of Gammarus oceanicus. Two types of cells are described: germinal (oogonia, oocytes) and interstitial. A comparison is made of the fine structure of oogonia, early and advanced maturing oocytes and mature oocytes. Two types of inclusions, cortical granules and lipid droplets, are produced by maturing oocytes, and remain in the cytoplasm of mature oocytes within the ovovitelline duct lumen while only lipid droplets are evident in the oocyte cytoplasm of intrauterine eggs. The fate and possible functions of both inclusions are discussed. The interstitial component of the ovary is a syncytium. The maturing oocyte surface is prolonged into lamellae, forming a lamellar mesh with adjacent germ cells and close association of interstitial mitochondria. Deep invaginations of the ovarian basement layer between numerous folds of ovarian lobules facilitate close contact of the interstitium and sarcoplasmic glycogen-rich processes with maturing oocytes. Synchronism in maturity among all of the oocytes in the ovary is shown at different stages of oogenesis. Such a pattern of oogenesis results in the production of many eggs at the same stage of development and is considered an adaptation for the dissemination of fertilized eggs that occurs only at the death of the gammarid host.
4

Vitellocyte ultrastructure in the cestode Didymobothrium rudolphii [Monticelli, 1890]: possible evidence for the recognition of divergent taxa within the Spathebothriidea

80%
Poddubnaya L. G., Gibson D. I., Swiderski Z., Olson P. D.
Acta Parasitologica
|
2006
|
tom 51
|
nr 4
In the spathebothriidean tapeworm Didymobothrium rudolphii (Monticelli, 1890) the fine structure of the vitellocytes at different stages of their development within the vitelline follicles, vitelline ducts and uterus was studied for the first time using transmission electron microscopy. The vitellocyte inclusions of D. rudolphii are shell globule clusters containing tightly packed shell globules associated with a matrix of moderate electron density, glycogen granules, large electron-lucent lipid droplets (up to 3 μm in diameter), and, occasionally, a lipid droplet may occur in the nucleus of the vitellocytes. The diameter of the clusters ranges from 0.4 to 2.5 μm, the number of shell globules in the clusters varies from 8 to 45, and the size of the globules ranges from 0.12 to 0.25 μm and they are of approximately homogeneous sizes within a cluster. Most vitellocyte lipid droplets have a heterogeneous configuration with a ‘cavity’ inside them when they are within vitelline ducts and intrauterine eggs. Vitellocytes of the eggs contain dark concentric bodies and lipid droplets. The interstitial tissue has a syncytial structure. The morphological parameters of the diameter and shape of shell globule clusters, arrangement of shell globules in clusters, number and diameter of globules within clusters, types of lipid droplets and presence of dark concentric bodies are compared with those of two other spathebothriidean genera, Cyathocephalus and Diplocotyle. The comparative data demonstrate that vitelline material morphology has unique features in three spathenothriidean genera and may be used as evidence for the recognition of separate taxa.
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