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 optimum temperature for catalyses, Explain What is the optimum...

Explain What is the optimum temperature for catalyses? Ans) For any chemical reaction, the reaction rate enhances with temperature, so the higher the temperature, the earlier t

What is the gas exchange unit of the mammalian lungs, Q. What is the gas ex...

Q. What is the gas exchange unit of the mammalian lungs? The gas exchange units of the mammalian lungs are the alveoli. Q. What is the physical process through which gas ex

Heparin, HE P ARIN It is highly sulphated mucopolysaccharide made ...

HE P ARIN It is highly sulphated mucopolysaccharide made of alternate units of glucosamine and glucuronic acid. Heparin is mainly produced by liver and mast cells. I

Carbohydrate case study, CT is a 3 year old female who develops signs of hy...

CT is a 3 year old female who develops signs of hypoglycemia in the early morning unless she is fed during the night.  CT eats balanced meals for her age group during the day, with

Neural impulse is transmitted from one cell to another, What is the structu...

What is the structure through which the neural impulse is transmitted from one cell to another? What are its parts? The structure by which the neural impulse passes from one c

What are mutagenic agents, What are mutagenic agents? The Mutagenic age...

What are mutagenic agents? The Mutagenic agents, or mutagens, are physical, chemical or biological factors that can cause alteration in DNA molecules. Instances of believed

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

How we write assimgment about mycobiology of mycoplasma in detail

Treatment and nursing management of cleft lip, Treatment and Nursing Manage...

Treatment and Nursing Management The initial treatment is surgical repair of  the cleft. The timing of the repair varies from surgeon to surgeon, but most prefer cleft lip rep

Phyla of protists, 1 list the names of the phyla of animalike protists that...

1 list the names of the phyla of animalike protists that have only free-living members

Define corneal ulcer - micronutrient deficiencies, Define Corneal Ulcer - M...

Define Corneal Ulcer - Micronutrient Deficiencies? Corneal xerosis, if not treated promptly, leads to ulceration of the cornea. Initially, the ulcer may be shallow, and if it b

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