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

Water reuse and recycling, Water Reuse And Recycling Are Becoming   Much Mo...

Water Reuse And Recycling Are Becoming   Much More Common As Demands For Water Exceed Supply. Unplanned reuse occurs as the result of waste effluents entering receiving waters or g

Phylum , General characteristics of phylum

General characteristics of phylum

Define regulation and excretion of sodium and chloride, Define Regulation a...

Define Regulation and Excretion of sodium and chloride? Renal excretion and retention of these elements is closely regulated. The total content of body sodium especially the co

Explain beginning and the end of the third interphase period, Q. What are t...

Q. What are the events that mark the beginning and the end of the third interphase period? What happens in the cell in this period? The third interphase period is the G2, It be

Explain energy requirement during tuberculosis, Explain Energy requirement ...

Explain Energy requirement during tuberculosis Energy  :  The criteria to establish  the energy intake is the body weight status coupled with the rise  in body temperature. Con

Biology in ancient india, BIOLOGY IN ANCIENT INDIA - L A T E STONE ...

BIOLOGY IN ANCIENT INDIA - L A T E STONE AGE [10,000 - 20, 000 B.C) Man first cultivated wheat, barley, lentils & peas. In India rice was first cultivated at Meherga

Which type of energy is used in photosynthesis transformed, Q. Into which t...

Q. Into which type of energy is the light used in photosynthesis transformed? The luminous energy used in the photosynthesis is transformed in to the chemical energy.

Radiation cataract and steroid induced cataract of the eye, Explain the rad...

Explain the radiation cataract and steroid induced cataract of the eye. Radiation Cataract Exposure to radiation causes discoid posterior sub-capsular opacities. Mechanism o

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