Colonial theory - metazoa, Biology

Assignment Help:

Colonial Theory - Metazoa

 This is the most popular theory on the origin of Metazoa. The idea was conceived by Haeckel (1874) modified by Metschnikoff (1886) and revived by Hyman (1940). This theory considers the flagellates to be the most probable ancestral group of metazoans. For support of this theory the following evidences are cited:

 1) Flagellated spermatazoa occur throughout the metazoan series.

2) Monoflagellated cells (with a single flagellum) are also common in lower metazoans (especially among sponges and coelenterates).

3) True sperms and eggs (feature of metazoans) are present in phytoflagellates.

4) Phytoflagellates also display a type of colonial organization that could have led to a multicellular construction. In fact, differentiation between somatic and reproductive cells has been attained in Volvox. Although Volvox is often used as a model for the flagellated colonial ancestor, it is not the likely ancestor of metazoans. Ultrastructural evidence points to the choanoflagellates (a small group of animal like flagellates) as the probable ancestor. Choanoflagellates have mitochondria and flagellar structures very similar to those in metazoan cells. Also choanocytes i.e. cells with a collar of microvilli are found in a number of groups of metazoans notably the sponges.


Related Discussions:- Colonial theory - metazoa

What is ezetimibe, It is a newer agent that inhibits cholesterol absorption...

It is a newer agent that inhibits cholesterol absorption by the enterocyte. It reduces cholesterol absorption by the enterocyte. It reduces cholesterol absorption by 23 per cent-50

Define role of polyunsaturated fatty acids - gene expression, Define Role o...

Define Role of polyunsaturated fatty acids - Gene Expression? In contrast, polyunsaturated fatty acids (PUFA) inhibit G6PD in both intact animals and in primary hepatocytes in

Salmonellosis, Salmonellosis The genus Salmonella comprises nearly 2500...

Salmonellosis The genus Salmonella comprises nearly 2500 serovars, traditionally based on Kauffman-White scheme in which H (flagelar) and O (somatic) antigens determine the ser

History of cell biology, HISTORY OF CELL BIOLOGY Scientific knowledge gro...

HISTORY OF CELL BIOLOGY Scientific knowledge grows with the development of new tools and techniques for studying various physical and biological processes. This is true also of t

Excretory system - urinary bladder, URINARY BLADDER - Pear shaped sac l...

URINARY BLADDER - Pear shaped sac like. Situated in pelvic region of abdominal cavity. Ventrally placed. Lined by transitional epithelum. Detrusor muscle i.e. to expell out

Phylum protozoa, what is the classificatin of phylum protozoa with orders

what is the classificatin of phylum protozoa with orders

Explain emulsifying properties of proteins, Emulsifying properties of prote...

Emulsifying properties of proteins  Proteins are the surface-active substances, which are extensively used in the food industry as emulsifiers to manufacture products such as d

Explain deteriorative changes in fats and oils, Explain Deteriorative chang...

Explain Deteriorative changes in fats and oils The food products undergo changes in flavour due to the chemical changes occurring in fats and oils present in them. The causativ

Control of soil pollution, Following steps must be taken: Domestic an...

Following steps must be taken: Domestic and industrial garbage should be profitably utilized. Compost pits and installation of Gobar-gas plant in rural areas must be encourag

Iron deficiency anaemia, Iron Deficiency Anaemia   This is the most com...

Iron Deficiency Anaemia   This is the most common nutritional and haematologic disorder  in infancy and chhildhood in developing countries. It is caused by lack of sufficient i

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