In the viviparous monogeneans like Gyrodactylids, embryos develop serially one inside another within the parental uterus, a phenomenon referred to as serial polyembryony. In these, development occurs via two routes: first-born daughters develop at the centre of an embryo cluster in utero, whereas all other daughters develop from oocytes. The resulting offspring are, however, morphologically indistinguishable.
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http://www.sciencedirect.com/science/article/pii/S0020751901003307
Mohamed,
Whether there is true viviparity in any monogenean or other platyhelminth is a matter of controversy, if the term is applied as in the case of placental mammals. True placenta-like connections have been reported, but none has been documented unequivocally. Most monogeneans, cestodes, and trematodes are either oviparous or ovoviviparous. The latter situation occurs when full development of the larva (miracidium for digeneans or hexacanth for cestodes) occurs within the maternal uterus. In all such cases that are fully documented, the embryo receives nutrients from stores in the vitellocytes and/or oocytes, but not from the uterus or other somatic portions of the maternal reproductive system. The uterus has been shown definitely to contribute to such things as egg shells and extraembryonic protective tissues, but not to embryo nutrition, which would be required for true viviparity to exist. I have listed below some of our work on this topic, which has been extensive for many years regarding digeneans and cestodes. My research group has not worked directly with monogeneans, but we have followed the work of others closely. If you want more papers, just let me know and I will get them to you.
Best wishes,
Bruce
Bruce
Data A standardised terminology of the embryonic envelopes and as...
Article Ultrastructure of the early gravid uterus of Corallobothrium...
Article Ultrastructural study of the egg wall surrounding the develo...
Article Ultrastructural evidence for completion of the entire miraci...
Article Fine Structure of the Gravid Paruterine Organ and Embryonic ...
Data Conn 2007 Recent Advances in the Reproductive and Developmen...
Article Recent advances in the reproductive and developmental biolog...
Article Morphology and fine structure of the gravid uterus of three ...
Book Atlas of Invertebrate Reproduction and Development, Second Edition
Article Functional ultrastructure of the parenchymatic capsules of t...
The phenomenon of viviparity in monogeneans is also called pedogenetic polyembryony as the youngs inside the uterus of the adults have a "next generation baby" inside
Well, viviparous phenomenon is still debatable ... It needs more research...
Apart from Gyrodactylids, which other monogeneans show viviparity.. Does Diplozoon spp show this phenomenon?
it is called pedogenetic polyemberyony as youngs inside uterus of mother
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