Syncytial theory - metazoa, Biology

Assignment Help:

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.


Related Discussions:- Syncytial theory - metazoa

What is consanguineal marriage, What is consanguineal marriage? Why is the ...

What is consanguineal marriage? Why is the appearing of genetic disease more probable in the offspring of a consanguineal marriage? Consanguineal marriage is the marriage among

Individuals with tyrosinenmia, Individuals with tyrosinenmia have food patt...

Individuals with tyrosinenmia have food patterns very similar to the one for PKU discussed above. PKU is more common than tyrosinemia. Foods that are high in tyrosine and phenylala

What are the advantages of the closed circulatory system, What are the adva...

What are the advantages of the closed circulatory system over the open circulatory system? The closed circulatory system is more efficient. As blood circulates only inside bloo

Predation and coevolution, You now know that natural seleqtion aims at evo...

You now know that natural seleqtion aims at evolving adaptations of organisms in response to environmental changes in the inanimate world. Also many adaptations arise due to intera

How does the body defend itself from microorganisms, Q. How does the body d...

Q. How does the body defend itself from microorganisms and other harmful substances that enter the airway during the breathing process? The epithelium of the airway is a ciliat

Explain isolated chloroplast thylakoids, In an experiment, isolated chlorop...

In an experiment, isolated chloroplast thylakoids were incubated at pH 4.0 with ADP and inorganic phosphate (Pi) added to the medium and then transferred to a medium having pH 8.0.

How different are the ureotelic and the uricotelic excretion, Comparing tox...

Comparing toxicity and the requirement for dilution in water how different are the ureotelic and the uricotelic excretions? What are some examples of animals that present these res

Peptide bond, PEPTID E BOND Peptide or amide bond is a linkage es...

PEPTID E BOND Peptide or amide bond is a linkage established condensation reaction between amino group of one amino acid and carboxylic group of the second amino acid.

What is suprasternal views in echocardiography, Q. What is Suprasternal Vie...

Q. What is Suprasternal Views in echocardiography? To complete the echocardiography in the patients with CHD these views are essential. For optimal windows patient should lie

Assessment of peripheral vascular perfusion (beside test), Assessment of Pe...

Assessment of Peripheral Vascular Perfusion (Beside Test) Burger's Postural Test Perform in daylight.  Place patient supine with both legs elevated and knees

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd