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 the neurotransmitter of the neuromuscular junction, Q. What is the ...

Q. What is the neurotransmitter of the neuromuscular junction? How does the nervous system trigger muscle contraction? The nervous cells that trigger the muscle contraction are

Mycroboilogy mycoplasma, How we write assimgment about mycobiology of mycop...

How we write assimgment about mycobiology of mycoplasma in detail

Explain the terms - sulphur and boron, Sulphur and Boron Boron is extra...

Sulphur and Boron Boron is extracted with hot water. Sulphur is extracted with 500 ppm solution of P solution (prepared from potassium dihydrogen orthophosphate or monocalcium

What is the life cycle of the gymnosperms, What is the life cycle of the gy...

What is the life cycle of the gymnosperms? As all plants they show a diplobiontic life cycle, i.e., alternation of generations with diploid and haploid stages. The lasting (fin

Metaphase chromosomes, Metaphase chromosomes: Each metaphase chromoso...

Metaphase chromosomes: Each metaphase chromosomes is a duplicated structure which consists of two sister chromatids, attached at a point called centromere or primary constric

Explain the molecular level, We just had to clean a food freezer in the off...

We just had to clean a food freezer in the office because *someone* put a can of Coke in the freezer and it exploded. Explain, at the molecular level, why the Coke can exploded. A

Determine about the klove grooved pegboard test, Determine about the Klove ...

Determine about the Klove Grooved Pegboard Test The subject must place pegs shaped like keys into a board having recesses that are oriented in randomly varying directions. The

Relevance of biology to agriculture, ways in which modern agricultural acti...

ways in which modern agricultural activities may threaten survival species

Digestive gland, which system give the signals to salivary gland

which system give the signals to salivary gland

Explain gluten-free diet, Explain Gluten-free diet Gluten-free diet : ...

Explain Gluten-free diet Gluten-free diet : It is a diet recommended for the patients with gluten enteropathy. Gluten is present in wheat, rye, barley and oats. Thus, foods co

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