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

Animal nutrition, briefly explain the following feeding mechanisms in holoz...

briefly explain the following feeding mechanisms in holozoic animals a) filter feeding b) fluid feeding c)deposit feeding

What a cell with a euploid number of chromosomes contains, A cell with a eu...

A cell with a euploid number of chromosomes contains: A.one half of a complete set of chromosomes B.several complete sets of chromosomes C.the correct number of chromosomes D.two c

Of what importance are lactic acid fermentation to the cell, Of what import...

Of what importance are lactic acid fermentation and alcoholic fermentation to the cells that use these pathways? These pathways regenerate NAD, which the cells can use to keep

Causes of apomixis, Causes of Apomixis Apomictic species are generall...

Causes of Apomixis Apomictic species are generally hybrids or polyploids, as a consequence, there is irregular meiosis. Apomixis appears to be controlled by a set of genes. T

Issues impacting health and development - inequity, Normal 0 fa...

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

Can the cooler have had any effect, Write down any other possible explanati...

Write down any other possible explanations you think of.could the cooler have had any effect? Could something in the water be reasonable? Could there be an object in the water that

What is metallic implants, What is Metallic implants Metallic implants ...

What is Metallic implants Metallic implants undergo one or more several surface modifications to enable them to become suitable for implantation. These modifications are passiv

Biological properties of protoplasm, BIOLOGICAL PROPERTIES OF PROTOPLASM - ...

BIOLOGICAL PROPERTIES OF PROTOPLASM - 1 .       Respiration - Oxidation of food to liberate energy is respiration. Every living beings respire but every living beings do no

Define aerobic respiration, Where in mitochondria does the process called r...

Where in mitochondria does the process called respiratory chain happen? Which are the products of the Krebs cycle used in that final phase of the aerobic respiration? Respirat

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