@article {1495, title = {Investigation of the ultrastructure of Dendrocoelum constrictum (Platyhelminthes, Tricladida) spermatogenesis and mature spermatozoa}, volume = {337}, year = {2014}, month = {2014/9//}, pages = {513 - 520}, abstract = {

To add to our understanding of dendrocoelid spermatozoa and to describe additional phylogenetic characters, the ultrastructure of the testis was investigated in the subterranean freshwater planarian Dendrocoelum constrictum. This is the first study investigating spermatogenesis and spermatozoon ultrastructure in a subterranean freshwater planarian species. We found that the basic structure of spermatozoa in D.\ constrictum is similar to that of other Tricladida that have been studied previously. In fact, D.\ constrictum spermatozoa possess an elongated nucleus, one giant mitochondrion, and two subterminal flagella with a 9 + \‘1\’ pattern. The flagella emerge together from one side of the spermatozoon. However, D.\ constrictum has some characteristics that have not yet been described for other freshwater planarians. In fact, the number of cortical microtubules reaches the maximum number in the anterior and middle part of region I, and then decrease until they disappear towards the posterior extremity of the spermatozoon. The extreme tip of the anterior region of the spermatozoon exhibits a specific external ornamentation of the plasma membrane.

}, keywords = {Dendrocoelum constrictum, Free-living flatworm, Mature spermatozoon, Spermatogenesis, Ultrastructure}, isbn = {1631-0691}, url = {http://www.sciencedirect.com/science/article/pii/S1631069114001632}, author = {Harrath, Abdel Halim and Gammoudi, Mehrez and Mansour, Lamjed and Ahmed, Mukhtar and Sirotkin, Alexander V. and Al Omar, Suliman Y. and Ibrahim, Khalid E. and Alwasel, Saleh H.} } @article {392, title = {An ultrastructural study of oogenesis and cell dynamics during cocoon shell secretion in the subterranean freshwater planarian Dendrocoelum constrictum (Platyhelminthes, Tricladida)}, journal = {Tissue and Cell}, volume = {45}, year = {2013}, month = {02/2013}, pages = {39 - 46}, abstract = {

The ultrastructure of the ovary and the female atrium during cocoon formation was investigated in the subterranean freshwater planarian Dendrocoelum constrictum. In the peripheral portion of the ovary, the oogonia are recognized as undifferentiated germ cells, which are morphologically similar to neoblasts that have a high nucleus/cytoplasm ratio. Oocyte maturation is characterized by a marked growth of the cytoplasm because of the accumulation of cytoplasmic organelles and inclusions. The Golgi complexes begin to increase within the ooplasm and produce vesicles with an electron-dense content that fuse to produce larger spherical globules with homogeneous and electron-dense material. In the mature oocyte, the spherical globules migrate toward the cortical ooplasm, forming a continuous monolayer. We confirm that these spherical globules, which represent cortical granules rather than eggshell globules, vary in size up to 2 \μm and their electron-dense content shows concentric thin bands. After leaving the ovary through the oviduct, the mature and fertilized oocytes reach the female atrium where they are packaged with thousands of vitelline cells in the cocoon shell. Based on our ultrastructural analysis, we demonstrate that the wall of the cocoon shell is composed of two layers, each of which has a different origin. The shell granules extruded from the vitelline cells are involved in the secretion of the inner layer of the cocoon shell, whereas the outer layer of the cocoon shell is synthesized by the epithelial cells in the genital atrium.

}, keywords = {Cocoon, Cortical granules, Dendrocoelum constrictum, Oogenesis, Turbellarian, Ultrastructure}, isbn = {0040-8166}, url = {http://www.sciencedirect.com/science/article/pii/S0040816612000845}, author = {Harrath, A. H. and Ahmed, M. and Sayed, S.R. and Saifi, M.A. and Alwasel, S.H.} }