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

Define platyhelminthes - larval stages of fasciola hepatica, Platyhelminthe...

Platyhelminthes - Larval Stages of Fasciola Hepatica and Taenia Solium? You have already studied the representative species of classes Turbellaria, Trematoda and Cestoda of Ph

Explain about coronaru heart diseases, Q. Explain about Coronaru Heart Dise...

Q. Explain about Coronaru Heart Diseases? Coronary heart disease is a broad term comprising of a spectrum of diseases associated with disorders of the circulation, heart muscle

Define sugar as a type of carbohydrates, Define Sugar as a type of Carbohyd...

Define Sugar as a type of Carbohydrates? This group includes monosaccharide and disaccharides. List down the names of sugars under both these groups and check it out with those

Neontology, Neontology : It is the study of recently formed organisms. Neon...

Neontology : It is the study of recently formed organisms. Neontology science is the part of biology that is in contrast to paleontology. Neontology science deals with now living o

Prevention of outbreak in salmonellosis, Q. Prevention of Outbreak in salmo...

Q. Prevention of Outbreak in salmonellosis? Prevention of Outbreak: The control of food borne salmonella infection requires the following: 1. Preventing food contamination

Explain the process of nuclear reorganization, Process of nuclear reorganiz...

Process of nuclear reorganization in protozoa in which nucleus divides, each half undergoes a maturation, and two persisting functional nuclei reunite is termed as: a) Autogamy

How cholera is generally spread in humans, How cholera is generally spread ...

How cholera is generally spread in humans Associated Foods: Cholera is generally a disease spread by poor sanitation, resulting in contaminated water supplies. Sporadic cases o

Mendel''s second law not for two or more phenotypical traits, Why is not Me...

Why is not Mendel's second law always valid for two or more phenotypical traits of an individual? The Mendel's second law, or the law of the independent assortment, is valid fo

Diversity in living organisms, why is it necessary to classify living organ...

why is it necessary to classify living organisms ? what are the advantages of classifying organisms?

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