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

Mechanism of enzyme action, Mechanism  of Enzyme Action  The action of...

Mechanism  of Enzyme Action  The action of enzymes is to lower  the activation energy  or threshold  of their substrates which. Therefore  become  activated and   react  with

What is simple transposition in neonates, What is Simple Transposition in N...

What is Simple Transposition in Neonates ? A baby with this malformation needs to be operated without delay. A very cyanosed infant will require palliation by balloon arteries

Skin., what is the difference between fair skin and dark skin?

what is the difference between fair skin and dark skin?

Define factors that lead to vitamin k deficiency, Define Factors that Lead ...

Define Factors that Lead to Vitamin K Deficiency? The factors that lead to vitamin K deficiency include: 1) Marginal dietary intake if one undergoes trauma and extensive sur

Explain about the saccharin - artificial sweeteners, Explain about the sacc...

Explain about the saccharin - artificial sweeteners? The oldest artificial sweetener is saccharin (the calcium or sodium salt of 1, 2- benzisothiazol-3(2H)-one 1, 1-dioxide) as

Gases, GASES There are 4 gases in the protoplasm which remain dissol...

GASES There are 4 gases in the protoplasm which remain dissolved in its free water. These 4 gases are follows-                  CO 2     >  O 2  > N 2  > H 2

Determine the modification of native starch, Determine the Modification of ...

Determine the Modification of native starch Modification of native starch can be either physical or chemical. Chemical modification includes reaction of starch with  acid or al

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