Colonial theory - metazoa, Biology

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.

Posted Date: 1/15/2013 2:55:12 AM | Location : United States







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

Write discussion on Colonial theory - metazoa
Your posts are moderated
Related Questions
Describe about the Argyll Robertson Pupil (ARP) Argyll Robertson Pupil (ARP) occurs in patients who have tertiary syphilis. There is a "light-near dissociation" because pupils

Critical Thinking Why is it necessary to use the same restriction enzyme to cut two pieces of DNA that are to be joined together? As each restriction enzyme recognizes a specif

MUCOPROTEIN S (GLYCOPROTEINS) Proteins having conjugated mucosaccharides that form viscous mucus or mucoid secretions. The gastric mucus or mucoprotein is resistant to p

Use the genetic code table Assignment34 The codon GCA specifies which amino acid?

Dose-scaling Toxicological equivalent doses in animals and humans are a debatable issue. The Joint FAOIWHO Expert Committee on Food Additives (JECFA) and Joint FA01 WHO Meetin

Q. What are the two major ions that participate in the electrical impulse transmission in neurons? The two major ions that participate in the electrical impulse transmission in

Explain the Classification of simple proteins? 1) Albumins: Proteins such as egg albumin and serum albumin are soluble in water and coagulable by heat. 2) Globulins: These p

Define Various Methods of Food Processing? In this unit, you studied the various methods of food processing. You learnt that food being most vital for the survival of human bei

Until the Krebs cycle, aerobic respiration can be explained without mentioning oxygen, the chemical element after which the reaction gets its name. Where in the process does this c

Q. What is Interpretation of Stress Echocardiography? The standard approach to interpretation is qualitative. The attendant need for training and problems posed for reproducibi