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 rate of photosynthesis in c3 plants, What would happen to the rate ...

What would happen to the rate of photosynthesis in C3 plants if the CO2 concentration level almost doubles from its present level in the atmosphere?

Theories to explain fine structure of chromosome, THEORIES TO EXPLAIN FINE ...

THEORIES TO EXPLAIN FINE STRUCTURE OF CHROMOSOME (1 ) Multistranded theory Steffenson 1959 - each chromosome composed of two chromatids (Half Chromosome) and each chromat

List the heterotrophic nutrition in plants, a) List the a variety of modes ...

a) List the a variety of modes of heterotrophic nutrition in plants. b) Define any two modes giving one example of each.

Gonads and ovary - reproduction, Normal 0 false false false...

Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

Explain nsp and food hydrocolloids, NSP NSP or dietary fibre is the nam...

NSP NSP or dietary fibre is the name given to a group of materials found in the cell walls of plants which gives the plant its structure and form. Food hydrocolloids Fo

Hindbrain - cerebellum, HIND BRAIN - 1 .       CEREBELLUM - Li...

HIND BRAIN - 1 .       CEREBELLUM - Little part, lies below the posterior part of cerebrum & above the medulla oblongeta. It conists of median lobe vermis & 2 lat

Proteins of plant origin - seed proteins, Proteins of Plant Origin - Seed P...

Proteins of Plant Origin - Seed Proteins Seed Proteins: Although a large number of plants produce seeds having protein contents in excess of 15%, only a few are utilized for fo

Vector for cloning genes into higher organisms, Which one of the following ...

Which one of the following is used as vector for cloning genes into higher organisms ? 1. Baculovirus 2. Salmonella typhimurium 3. Rhizopus nigricans 4. Retrovirus

Can mitosis occur in haploid cells, Can mitosis occur in haploid (n) cells?...

Can mitosis occur in haploid (n) cells? And in triploid cells? The mitotic cell division can happen in haploid (n) cells, diploid (2n) cells, triploid (3n) cells, etc. Mitosis

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