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

Special structures of the avian digestive tube, Q. What are the special str...

Q. What are the special structures of the avian digestive tube and their respective functions? The crop has the function of temporary storage of ingested food and it is a more

Explain some important phospholipids, Explain some important phospholipids ...

Explain some important phospholipids The chemical structure of  phosphatidylcholine (lecithin) illustrated here in Figure is  typical of  the phosphatides  found in the brai

Show geniculate bodies of the thalamus, Q Show Geniculate Bodies of the tha...

Q Show Geniculate Bodies of the thalamus? THALAMUS - two large circular shaped masses at "roof" of 3rd brain ventricle. Contains many different nuclei which function as relay

Evolution, Evolution can be explained as follows  1) The change in the ...

Evolution can be explained as follows  1) The change in the life over time by adaptation, over-reproduction, variation and differential survival/reproduction, a procedure refer

What is plaque, What is plaque? Plaque is a film over the teeth and hav...

What is plaque? Plaque is a film over the teeth and having of saliva, mucus, bacteria and the substances they produce. It may also have mineral salts of calcium and magnesium.

Spinal cord sectioned at the cervical level, Q. How is it explained that a ...

Q. How is it explained that a person with the spinal cord sectioned at the cervical level is still able to perform the patellar reflex? The arch reflex depends only on the inte

The permissible use of the technique amniocentesis, The permissible use of ...

The permissible use of the technique amniocentesis is for: 1. detecting sex of the unborn foetus 2. artificial insemination 3. transfer of embryo into the uterus of the su

Define vitamin k-dependent carboxylation, Define Vitamin K-dependent carbox...

Define Vitamin K-dependent carboxylation? Vitamin K acts as a cofactor in the synthesis of g-carboxyglutamic acid (Gla) from glutamic acid residues required for the normal coa

Phylum, morphological characterstics of e histolytica

morphological characterstics of e histolytica

Define the term - lamellac, Define the term - lamellac The inner membr...

Define the term - lamellac The inner membrane is folded into very closely packed membranes called the lamellac. The lamellae flatten out at regular intervals into structures c

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