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

Determine the meaning of response cost, Determine the meaning of Response c...

Determine the meaning of Response cost This is a type of punishment in which the subject has to return back the token (positive reinforcement) earned earlier if the subject dis

What are the haversian canals, What are the Haversian canals and the Volkma...

What are the Haversian canals and the Volkmann's canals of the bones? Is the osseous tissue vascularized? The Haversian canals are longitudinal canals show in the osseous tissu

Explain precautions for morphological study of fungi, Explain Precautions f...

Explain Precautions for Morphological Study of Fungi? 1. Use sterile forcep and needles for slide culture technique. 2. Aseptic conditions should be maintained.  3. Caref

Polypeptide chains of hemoglobin, Q. In sickle cell anemia, a hereditary di...

Q. In sickle cell anemia, a hereditary disease, there is replacement of one amino acid by another in one of the four polypeptide chains of hemoglobin. In this case are all of the s

Guess the number of different haploid cells, A diploid cell contains four p...

A diploid cell contains four pairs of homologous chromosomes designated C1 and C2, M1 and M2, S1 and S2, and W1 and W2. Predict the number of different haploid cells that could be

Difference between essential and natural amino acids, What is the differenc...

What is the difference between essential and natural amino acids? Ans) Significant amino acids are those that the organism is not able to synthesize and that require to be inges

Find the magnitude of the acceleration of the proton, A proton accelerates ...

A proton accelerates from rest in a uniform electric field of 650 N/C. At some later time, its speed is 1.3 106 m/s. (a) Find the magnitude of the acceleration of the proton. m/s2

Cation exchange capacity, Cation Exchange Capacity The adsorption of a ...

Cation Exchange Capacity The adsorption of a cation by a colloid nucleus or micelle and the accompanying release of one or more ions held by the micelle is termed as 'cation ex

Chromosomal type-genetic basis of sex determination, Chromosomal Type-Genet...

Chromosomal Type-Genetic basis of Sex Determination It refers to the condition where the genes involvcd in sex dcterrnincltion arc located on specific chromosomes known as the se

Stock concentration of dopamine, a) A cat has just arrived to the veterinar...

a) A cat has just arrived to the veterinary clinic with low blood pressure. The cat weighs 5 kg, and as the on call Vet you want to use a bag of saline to prepare a dopamine drip f

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