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

Topic test, In what way do investigations build scientific knowledge?

In what way do investigations build scientific knowledge?

Amphetamines, AMPHE T AMINE S - Commonly called pep pills or anti...

AMPHE T AMINE S - Commonly called pep pills or antisleep drugs. They increase physical & mental performance. Taken by truck drivers, student & night workers to keep

Determination of neural ectoderm by induction, Determination of Neural Ecto...

Determination of Neural Ectoderm by Induction Earlier you know that the dorsal mesoderm induces the ectoderm to differentiate into neural tissue. Spemann and his co-workers co

How many asymmetric the amino acid serine have, How many asymmetric carbons...

How many asymmetric carbons does the amino acid serine have? Please explain with a strucutral diagram if possible.

Cardiac catheterization and angiography, Q.Define Cardiac catheterization a...

Q.Define Cardiac catheterization and angiography? The purpose of this unit is to give you an overview and insight into the world of Cardiac Catheterization and Angiography. Thi

Explain about gamma diversity, Q. Explain about gamma diversity? Gamma ...

Q. Explain about gamma diversity? Gamma (g) richness refers to the rate of change across larger landscape gradients and gamma diversity is a measure of the overall diversity fo

Zygotic or suspensor polyembryony, Zygotic or Suspensor Polyembryony ...

Zygotic or Suspensor Polyembryony Cleavage of the apical cells of the globular or filamentous proembryo produced by the zygote may result in two or more embryos in a seed. Th

Soil-environmental components, Soil-Environmental Components The word s...

Soil-Environmental Components The word soil is derived from Latin word 'solum' meaning earthy material in which plants grow. The soil is the consolidated outer layer of the ear

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