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
Q. How different are the swimming strategies in chondrichthyes and in osteichthyes? Why do sharks need to agitate their body to swim while bony fishes do not? Bony fishes have

Plate Tectonic Is a Theory of Geology Which describes the large scale motion of earth's lithosphere. The theory builds on the older theory of continental drift from the first half

Which pair of glands is affected by the hormones from the posterior pituitary? A) thyroid, ovaries B) adrenal cortex, liver C) testes, mammary glands D) kidneys, uterus

What is Infra-diaphragmatic Type of TAPVC? Initial stages of operation are the same as for supracardiac type of TAPVC. The heart is lifted out of the pericardial cavity and c

Hiatus Hernia: In  this type of hernia, cardiac end of  the stomach passes through an abnormally wide oesophageal opening in the diaphragm  (see Fig. 2.6). Clinical manifestat

what are the economic importance of obelia?

Food Applications of hemicelluloses The hemicelluloses find their application in  food systems as emulsifer, stabilizer and binder in flavor bases, dressings and pudding mixes.

Why is genetic homozygosity dangerous to a nearly extinct species? Genetic homozygosity leaves no variation for natural selection to act on. Thus, a new disease could wipe

The Waldorf family was caught in a fire but escaped. Unfortunately, the father and daughter suffered burns. The father had second-degree burns on his entire chest, abdomen, and bot

State the Diagnosis and prevention of VIBRIO PARAHAEMOLYTICUS Diagnosis: Diagnosis of gastroenteritis caused by this organism is made by  culturing the organism from the diarrh