Syncytial theory - metazoa, Biology

Syncytial Theory - Metazoa

This theory suggests that the ancestral metazoan was at ,first Syncytial in structure but later became cellularised by formation of cell membranes around individual nuclei this producing a typical multicellular body. Hadzi (1953) and Hanson (1977) have been the chief proponents of this theory. As many ciliates tend to have a bilateral symmetry, the advocates of this theory maintain that the ancestral metazoan was bilaterally symmetrical similar to the present day acoelous flatworms. The theory receives support from the fact that acoelous flatworms are

  1. Of the same size range as the ciliates,
  2. Are bilaterally symmetrical
  3. Are ciliated and
  4. Tend towards a Syncytial condition

532_Syncytial Theory.png

Figure: Possible routes for evolution of animals

There are several objections to this theory. It ignores the embryology of flatworms in which nothing similar to cellularization occurs, nor does it explain the presence of flagellated sperms in metazoans. Perhaps the most important objection to this theory is that it assumes that .acoelous flatworms are the most primitive metazoans and therefore, presumes bilateral symmetry to be more primitive than radial symmetry and thus radial coelenterates must have been derived from bilateral flatworms. But then it is accepted that radial symmetry is more primitive than bilateral symmetry and radial coelentrates could not have evolved from flatworms.

Posted Date: 1/15/2013 2:52:29 AM | Location : United States







Related Discussions:- Syncytial theory - metazoa, Assignment Help, Ask Question on Syncytial theory - metazoa, Get Answer, Expert's Help, Syncytial theory - metazoa Discussions

Write discussion on Syncytial theory - metazoa
Your posts are moderated
Related Questions
What is Mega sporogenesis

Q. Why does not a long lasting vaccine against common cold exist yet? Viruses that present a high mutation rate like the virus that causes the common cold escape easily from th

Define Discovery of other Essential Nutrients? Following the identification of the food factors involved in beriberi, pellagra and scurvy, the search was on for other water-sol

Give an example of how a functional group can affect the elements of an organic compound. The hydroxyl group on alcohols is polar and this produces alcohols polar compounds.

Explain about the Deficiency of Riboflavin? Riboflavin deficiency results in the condition of hypo- or ariboflavinosis, with soreĀ  throat, hyperaemia (condition in which the bl

Arteries - Circulation The arteries deliver blood from the heart. Figure shows the structure of arteries and the different layers of the vessel wall. The thick walls of these

Nursing Process Assessment History, precipitating factors, current medication, medication used to relieve asthma symptoms. Any recent changes in medication regimen.

Consider an axon of a neuron. At time=t1, its voltage is at threshold for an action potential; at time=t2, its voltage is at 0 millivolts prior to the peak of that action potential

What is antistaphylococcal prophylaxis and pseudomonas aeruginosa? I''m doing a project on cystic fibrosis, and I''m curious what these terms have to do with the disease. Thanks!

You ran both a body temperature and room temperature test for each enzyme you tested. Did the two temperatures seem to have an effect on the enzyme Exercise? Why or why not?