Origin and evolution of metazoa, Biology

Assignment Help:

Origin and Evolution of Metazoa

Most of the early metazoans were soft bodied and so their fossils are rare. The extremely fragmented fossil record does not shed any specific light on their origin. Therefore, 'most of the explanations on their origin are based on their embryology and -comparative morphology. A series of theories have been put forward to explain the origin of multicellular metazoans from unicellular organisms. Of these, three principal theories could be considered.

1) Syncytial Theory: That the ancestral metazoans have arisen from a multinucleate. ciliate by compartmentalization or cellularization.

2) Colonial Theory: That the ancestral metazoans have arisen from colonial flagellates by cellular specialisation and interdependency.

3) Polyphyletic Theory: That the metazoans have arisen from more than one group of organisms.


Related Discussions:- Origin and evolution of metazoa

What is parasitism, Q. What is parasitism? The Parasitism is the ecolog...

Q. What is parasitism? The Parasitism is the ecological interaction in which a being lives at the expense of another. The parasite often doesn't cause immediate death of the ho

Blood protozoan and ricketsial diseases - trypanosomiasis, B l oo d Prot...

B l oo d Protozoan and Ricketsial Diseases T r y p a n o s o m i a si s It is also known as surra in equines and tibarsa in camel and results in intermitte

Which substance does not contain hormones , Hormones are composed from seve...

Hormones are composed from several classes of molecules. As far as our present knowledge extends, hormones are not found in which of the subsequent categories of substances: a)

Which compounds results from cyclization of glucose, Which of the following...

Which of the following compounds results from cyclization of glucose? Select one: a. alpha-D-glucopyronose b. beta-D-glucopyronose c. alpha-D-glucofuranose d. beta-D

Define obesity - excessive fat intake, Define Obesity - Excessive Fat Intak...

Define Obesity - Excessive Fat Intake? In obesity, cutting down total energy intake or increasing output to ensure energy balance is the basic principle of prevention. Fat bein

Intravenous drug abusers, The risk for IE among IV drug abusers, 2 to 5 per...

The risk for IE among IV drug abusers, 2 to 5 per cent per patient- year, is estimated to be several fold greater than that of patients with rheumatic heart disease or prosthetic v

Oligosaccharides, OLIGOSACCHARIDES They are small-sized polymers of ...

OLIGOSACCHARIDES They are small-sized polymers of monosaccharides having 2 - 6 simple sugars, occasionally upto 9 - 10. Oligosaccharides are soluble in water, sweet to t

What are the main bryophyte groups, What are the main bryophyte groups? ...

What are the main bryophyte groups? The main bryophyte groups are the mosses, the liverworts and the hornworts. Image Diversity: mosses liverworts hornworts

Parasitology, how trematodes/nematodes adapt to their parasitic mode of fee...

how trematodes/nematodes adapt to their parasitic mode of feeding

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