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 concept of digestion of fats, Which of the following assist i...

Which of the following assist in the digestion of fats? A. Production of bile salts in the liver and the secretion of those bile salts into the small intestine. B. Emulsific

#ti ZOOLOGY , WHAT ARE SOME INFORMATION ABOUT HUMAN ZOOLOGY?

WHAT ARE SOME INFORMATION ABOUT HUMAN ZOOLOGY?

Define tests to measure flexibility component in the humans, Define Tests t...

Define Tests to Measure Flexibility Component in the Humans? The flexibility component measures the elasticity or range of motion around a joint. This component of physical fi

Explain about food processing and engineering, Explain about Food processin...

Explain about Food processing and engineering? Fundamental engineering concepts like momentum, heat and mass-transport systems; engineering aspects of food processing plant ope

What is the normal duration of the menstrual cycle, Q. What is the normal d...

Q. What is the normal duration of the menstrual cycle? How does the calendar contraceptive method work? The normal duration of the menstrual cycle is 28 days but it can vary am

State the term - focal seizures, State the term - Focal Seizures A foca...

State the term - Focal Seizures A focal seizure begins in one place and then spreads. As for example in a Jacksonian focal seizure, the attack begins with jerking movements in

Determine some indicators of malnutrition, Determine Some indicators of Mal...

Determine Some indicators of Malnutrition? A few of the indicators are enumerated below: 1. Indicators related to Government policies a. Nutrition policy b. Nutrition

Explain food applications of pullulan, Explain Food Applications of pullula...

Explain Food Applications of pullulan The food applications of pullulan include:  Due to its oxygen barrier properties, it can be used as a packaging material for fat /

Determine food sources of riboflavin - water-soluble vitamin, Determine the...

Determine the food sources of riboflavin? The food sources of riboflavin include: 1. Rich sources: Liver, dried yeast, egg powder, milk powder. 2. Good sources: Who

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