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

Amino acids and peptide bonds-protein structure, Amino Acids and Peptide Bo...

Amino Acids and Peptide Bonds, Protein Structure - The graduate can construct models of the structure and function of amino acids and peptide bonds, predict ionization of an amin

What are the main biological functions of water, Q. What are the main biolo...

Q. What are the main biological functions of water? Water is the basic solvent for chemical reactions of living beings; it is the main means of substance transportation in the

Pulmonary embolism, Systemic Infection Serious infections increase total...

Systemic Infection Serious infections increase total body metabolism and thus impose hemodynamic burden on the heart. Increased heart rate associated with infections is an addit

What is microtubules, What is Microtubules? Microtubules are the largest...

What is Microtubules? Microtubules are the largest intracellular fibers, with a diameter of about 25 nm (2.5 x 10-8 meters). They consist of hollow fibers composed of a protein

How is heart contraction triggered, Q. How is heart contraction triggered? ...

Q. How is heart contraction triggered? Heart contraction is independent from neuronal stimulus although it can be modulated by the autonomous nervous system in the heart there

PHYLUM MOLLUSCA, How we attempt a question of phylum mollusca?

How we attempt a question of phylum mollusca?

INVERTEBRATES - STRUCTURE & FUNCTION, 1. Write general characters of phylum...

1. Write general characters of phylum mollusca and classify it upto classes, giving at least two examples of each class.

Explain spoilage of cereals and cereal products, Q. Explain Spoilage of Cer...

Q. Explain Spoilage of Cereals and Cereal Products? Cereals are the main source of energy to human beings. There are several varieties of cereals, of which wheat and rice are t

Define measuring body composition - underwater weighing, Define Techniques ...

Define Techniques for Measuring Body Composition - Underwater weighing? Underwater weighing (densitometry): It applies the Archimedean principle of water displacement by the fu

Explain the nutritional and functional role of sulphur, Minerals :-  Sulfur...

Minerals :-  Sulfur Food Source       Widely distributed  Nutritional Functional role Essential nutrient: A constituent of the essential amino acids methionine and

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