Syncytial theory - metazoa, Biology

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.

Posted Date: 1/15/2013 2:52:29 AM | Location : United States

Related Discussions:- Syncytial theory - metazoa, Assignment Help, Ask Question on Syncytial theory - metazoa, Get Answer, Expert's Help, Syncytial theory - metazoa Discussions

Write discussion on Syncytial theory - metazoa
Your posts are moderated
Related Questions
What are the infructescences, pseudofruits and parthenocarpic fruits? The Infructescences are aggregated fruits formed from inflorescences, aggregated flowers. Grape clusters a

COMMON DISEASE OF GOATS - 1 .       ANTHRAX 2 .       FOOT & MOUTH DISEASE 3 .       CONTAGIOUS PNEUMONIA - Characterized by pneumonia & pleurisy, cough, snee

Q. What are the symptoms of Rheumatic Heart Disease? Symptoms generally appear after 1 to 6 weeks of the fever and sometimes the infection may have been too mild to have been r

The three charges in the are at the vertices of an isosceles triangle. Let q = 7.00 nC and calculate the electric potential at the midpoint of the base.

Because of developmental abnormality, the wall of left ventricle of an infant's heart is as thin as that of right ventricle. What would be its explicit effect on circulation of blo

Tuberculosis Tuberculosis is a specific communicable disease involving the pulmonary and extra- pulmonary tissues and is characterized by chronic clinical manifestations. The i

Thermal Stratification - Lake Ecosystem Shallow lakes show no thermal stratification as their waters are well mixed, resulting in uniform temperature throughout. However lakes

How is retaining wall works? A retaining wall together with the backfill the wall retains and the soil that supports the wall is a highly indeterminate system. The magnitudes o

Why Physical Activity is important for weight loss? You are already aware that exercise plays an important role in initiating and sustaining weight loss along with dietary and

two main evolutionary novelties presented by annelids