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

Alfieri repair-technique of operation, Alfieri Repair: This is advised ...

Alfieri Repair: This is advised for ischaenlic mitral regurgitation. In the area of prolapse, the anterior and posterior leaflet edges are approximated with one or two mattress

Explain the spectrophotometer or colorimeter, Explain the Spectrophotometer...

Explain the Spectrophotometer or Colorimete? These can be used to measure the microbial growth or can be used in various microbial and biochemical assays. Figure illustrates t

Class Pisces, need different types of information about fishes and their pi...

need different types of information about fishes and their pictures

Electrocardiography, ECG: Myocardial ischemia is indicated by T-wave invers...

ECG: Myocardial ischemia is indicated by T-wave inversions. Left ventricular hypertrophy (LVH) criteria: R in aVL >13 mm R voltage in L1+ S III >25 mm S v1 + R v5 or v6

Why is the o-h bond, Why would the O-H bond in C=O-H and the OH bonding wit...

Why would the O-H bond in C=O-H and the OH bonding with a water molecule be considered weak?

Explain ketogenic diet, Explan Ketogenic diet Ketogenic diet:   It is ...

Explan Ketogenic diet Ketogenic diet:   It is occasionally used to facilitate the control of epilepsy. Here, the patient  is  initially  fasted  for  48 hours and thereafter,

What is commensalism, What is commensalism? Commensalism is the ecologi...

What is commensalism? Commensalism is the ecological interaction in which one individual advantage while the other is neither benefited nor harmed. Commensalism is a harmonious

Explain lopinavir and its adverse effects, Explain Lopinavir/ritonavir  ...

Explain Lopinavir/ritonavir  Lopinavir is available in the US only in a fixed-dose combination with ritonavir . In treatment-naïve patients a regimen with lopinavir/ritonavir w

Explain working of refrigerator in microbiology laboratory, Explain the Wor...

Explain the Working of Refrigerator in Microbiological Laboratory? Refrigerator is a basic requirement in microbiological laboratory. It is used for maintaining microbial cultu

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