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

What is atom, What is atom? Atoms are the smallest component of matter ...

What is atom? Atoms are the smallest component of matter that determine its unique chemical and physical properties. They are composed of negatively charged electrons, positive

Codon, Codon is the group of three consecutive nucleotides within the mess...

Codon is the group of three consecutive nucleotides within the messenger RNA (mRNA) which encodes a message to initiate translation, to incorporate the specific amino acid into th

A useful way to grow seeds, A useful way to grow seeds Tie a piece of c...

A useful way to grow seeds Tie a piece of cloth over the mouth of an old potted meat jar. Permit extra cloth to hang down the sides and dip in about 2 cm of water contained in

State the process of metabotropic receptors, State the process of metabotro...

State the process of metabotropic receptors Consider a system that contains two neurons and one cardiac SA node cell in a culture dish bathed in normal physiological saline.  A

How do derived characters help cladistic taxonomists, How do derived charac...

How do derived characters help cladistic taxonomists determine phylogenetic relationships? A derived character is found only between members of a particular group. Thus, cladi

Explain the different types of cells in cell structure , Explain the differ...

Explain the different types of cells in cell structure ? Types of Cells :  Cells can be classified as being either prokaryotic or eukaryotic depending on whether or not a mem

protraction from hiv , Protraction from HIV  Under the following condi...

Protraction from HIV  Under the following conditions HIV is not transmitted 1) The secretions and body fluids like Saliva, Tears, Sweat, Faeces, and Urine have negligible HIV c

Define assessment of selenium status, Define Assessment of Selenium Status?...

Define Assessment of Selenium Status? Blood glutathione (GSH) peroxidase activity is directly related to blood selenium up to a level of 1.27 μmoles/L. Beyond this point, the a

Why is the occurrence of eyelids in amphibians, Q. Why is the occurrence of...

Q. Why is the occurrence of eyelids in amphibians in comparison to their absence in fishes an adaptation to terrestrial life? Eyelids associated to lacrimal glands protect and

Explain corrective surgery - endodontic surgery, Explain Corrective Surgery...

Explain Corrective Surgery - Endodontic Surgery perforation repair periodontal management (root resection, tooth resection) intentional reimplantation

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