Evolution of metazoa, Biology

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.
Posted Date: 1/15/2013 3:03:14 AM | Location : United States







Related Discussions:- Evolution of metazoa, Assignment Help, Ask Question on Evolution of metazoa, Get Answer, Expert's Help, Evolution of metazoa Discussions

Write discussion on Evolution of metazoa
Your posts are moderated
Related Questions
Explain Adverse effects of Zidovudine  It include anemia, neutropenia, nausea, vomiting, headache, fatigue, confusion, malaise, myopathy, hepatitis, and hyperpigmentation of or

In a cohort study that found an association between alcohol consumption and bladder cancer, 20,000 middle-aged men were asked about their drinking habits and then tracked for five

Q. Function of Glutamate? Glutamate It is the principal excitatory transmitter in the brain and is found throughout the central nervous system. Receptors Glutamate rec

What are biopolymers? Polymers are macromolecules made by the union of various smaller identical molecules, called monomers. Biopolymers are polymers present in the living bei

Define precaution for estimation of vitamin c in lemon juice? 1. Rinse all glassware with 3% metaphosphoric acid before you begin your practical and subsequently each time you

Q Do fishes present an closed or open circulatory system? How many chambers does a fish heart have? How does blood flow throughout the fish body? As in every vertebrate the cir

What is malnutrition? Malnutrition can be defined as a pathological condition resulting from a relative or absolute deficiency or excess of one or more of the essential nutrien

Angiosperms  are the flowering plants. They first appeared at least 110 million years ago from the unknown gymnosperm ancestor, these flowering plants have risen to dominance in th

WHAT IS THE TYPICAL REPRODUCTION CYCLE OF A DNA VIRUS

Gene targeting in ES cells: In some of the livestock species pro-nuclear injection cannot be used to modify the animals' own genes due to various reasons especially non availabil