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

Benefits of hand washing, Benefits of Hand washing You wash hands as a ...

Benefits of Hand washing You wash hands as a routine in daily life before cooking and eating food, after using wash room/toilet, before touching and caring a new born baby, aft

01.03 new technology, What is the best microscope to get a detailed view of...

What is the best microscope to get a detailed view of the parts inside of a preserved plant cell?

What are the main types of waste, Q. What are the main types of waste? ...

Q. What are the main types of waste? The waste can be classified into many kinds, each of them carrying its own different environmental problem: recyclable waste, organic waste

Mechanisms for response – protozoan, Mechanisms for Response – Protozoan ...

Mechanisms for Response – Protozoan Protozoa are sensitive to many kinds of stimuli like touch, temperature changes, light, chemicals, etc. It is not clear how they do so but

Filariasis, Filariasis Filariasis is a chronic infection caused by filarid...

Filariasis Filariasis is a chronic infection caused by filarid worms. Around 10 species of Filaridae family are parasitic to man. Adult worms live in the tissues or body cavities

Why does not gene therapy cure cystic fibrosis, Why doesn't gene therapy cu...

Why doesn't gene therapy cure cystic fibrosis? Although a normal gene is introduced into a patient's surface cells in the lung, these cells are not the ones that require produc

Life processes, mode of nutrition : out side the body

mode of nutrition : out side the body

Explain about the classification of fungi, Explain about the Classification...

Explain about the Classification of Fungi? The fungi, as you may recall reading above, is now placed in a separate kingdom called Myceteae. Traditionally, fungi were divided in

Define comprehensive dietary management regime of patient, Define Comprehen...

Define Comprehensive Dietary Management Regime of Patient? A comprehensive dietary management regime of the patient should be based on the patient profile as gathered pre and p

What are the uses of formycin b, What are the uses of formycin B? Formy...

What are the uses of formycin B? Formycin B is a drug used to demolish of intestinal parasites.

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