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

Skeleton, why do we get severe leg pains when the internal bone is cracked?...

why do we get severe leg pains when the internal bone is cracked?

Invertebrates, #question.3 different genera of invertebrates

#question.3 different genera of invertebrates

Explain the health economics, Explain the Health Economics? Health econ...

Explain the Health Economics? Health economics concentrates on application of the principles and rules of economics in the sphere of health. In broad terms, it includes analysi

Respiratory organs, Respiratory Organs These are the organs regarded ...

Respiratory Organs These are the organs regarded with the gaseous exchange, i.e., intake .of oxygen and output of carbon dioxide. They have generally greater rate of gas exch

Metabolic cataysis, Metabolic Cataysis A large number  of chemical reac...

Metabolic Cataysis A large number  of chemical reaction  occur  every  moment in a cell  to keep it. In the living  state, The rate  if  chemical  reaction normally depends upo

Deficiency diseases-vitamin- d deficiency, Vitamin- D deficiency Anima...

Vitamin- D deficiency Animals obtain vitamin D either through the diet or when skin is exposed to solar radiation. The deficiency of vitamin D is associated with reduced absor

Use of computer in biotechnology, what are the uses of computer in biotechn...

what are the uses of computer in biotechnology ??? briefly explain any twenty

What event marks the beginning of the menstrual cycle, What event marks the...

What event marks the beginning of the menstrual cycle? What is the blood concentration of FSH, LH, estrogen and progesterone in this phase of the cycle? By convention the menst

Difference between alpha glucose and beta glucose, What is the difference b...

What is the difference between alpha glucose and beta glucose? Why are they different?

GRADE 8 SCIENCE, what effects do human technologies have on our water syste...

what effects do human technologies have on our water systems?

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