Evolution of metazoa, Biology

Assignment Help:

Evolution of Metazoa

The sponges, coming under phylum Porifera are the closest to Protista, and can perhaps be regarded even as a colony of protists rather than being multicellular. No other group has evolved from them. The coelenterates consisting of the Cnidaria and the Ctenophora, which are both diploblastic and primarily radially symmetrical, can be regarded as truly the most primitive of the Metazoa. They have evolved from the ancestral planuloid metazoans as an offshoot:

1056_Evolution of Metazoa.png

Figure: Phylogeny of the animal kingdom

The Platyhelminthes (flatworms) have also evolved from planuloid ancestor. They do not have a coelomic cavity (acoelomates) but the mesoderm is cellular, they are triploblastic and are bilaterally symmetrical. This group and all higher Metazoa can be grouped as Grade Bilateria.

The pseudocoelomates phyla which include the nematodes and the rotifers are supposed to have evolved as an offshoot from the flatworms.

The Eucoelomata constitute the remainder of the Metazoa. The acoeloid flatworm like ancestors have given rise to two main stocks:

  1. The molluscan - annelidan, arthropodan stock with schizocoelous coelom.
  2. The echinoderm, hemichordate, chordate stock with enterocoelic coelom. The coelom serves as skeleton in the more primitive of the coelomates. Such as the polycheate worms, earthworms-etc. In arthropods and molluscs the coelom becomes reduced to the point of being represented by the cavity of the gonads. The other space in arthropod body is only a haemocael which is a mere space in the tissue filled with blood.

Related Discussions:- Evolution of metazoa

Name the system that contains three neurons, Name the system that contains ...

Name the system that contains three neurons Consider a system that contains three neurons in a culture dish bathed in normal physiological saline.  All three neurons are health

Embryology and histology, Embryology: Embryology (from Greek words embryon...

Embryology: Embryology (from Greek words embryon which means unborn embryo and logia which means study) is a branch of science which deals with the development of an embryo starti

What is the significance of axial skeleton, What is the significance of Axi...

What is the significance of Axial skeleton? The bones which make up skeleton of the main body axis of vertebrates. It comprise the cranium, vertebral column, and rib cages, How

What are coacervates, What are coacervates? Coarcervates are small stru...

What are coacervates? Coarcervates are small structures made of the aggregation of organic molecules under water solution. By electrical attraction the molecules join into bigg

Functions of ovary, Functions of Ovary The ovary of vertebrates perfor...

Functions of Ovary The ovary of vertebrates performs the following functions:   Production of eggs, Synthesis of hormones needed for the chemical coordination of repr

Best relates the severity and frequency of natural events, In general, whic...

In general, which of the following best relates the severity and frequency of natural events, such as storms or droughts? A) Nothing is known about this relationship. B) The severi

Coding sequence, Coding sequence is the portion of the gene or the mRNA wh...

Coding sequence is the portion of the gene or the mRNA which actually codes for a protein. Introns are not coding for the sequences; nor are the 5' or 3' untranslated regions (or

Define type of root canal perforations according to location, Define Types ...

Define Types of Root Canal Perforations According to location According to location (level) in relation to crestal bone): Coronal perforation: (supragingival) coronal to

Nursing assessment of acute glomerulonephritis, Nursing Assessment   Du...

Nursing Assessment   During assessment the child's parents will give you history of upper respiratory infection or skin infection  in the previous one to three weeks. Initially

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