Methods of grouping animals

 Methods of grouping animals

 

There are several ways of grouping animals. In all these methods the basic Taxon remains without any change. However the taxa are rearranged in different groups. All these groupings are mostly provided for the convenience in identifying similar taxa.

 

I. One of the earliest method of grouping the animals could be dividing the Animal kingdom into two assemblages called Invertebrata and Vertebrata.

This scheme was provided initially by Aristotle. This scheme does not have a place for the Prochordates.

 

II. Animals can also be grouped as single celled and multicellular. The single celled organisms are called the Protozoans. The multicellular could be called theMetazoans. In this arrangement among the metazoans the unique nature of the sponges in not having a tissue grade of body constuction is not mentioned.

 

III. In yet another method the animals are grouped under following three assemblages.

 

1.  Protozoa - single celled animals


2.  Parazoa - Multicellular without tissue grade (sponges).

 

3.  Eumetazoa - Multicellular with tissue grade.

 

Eumetazoa is a large group including most of the multicellular animals. Hence it is subdivided further into two groups.

 

1. Diploblastic animals - having ectoderm and entoderm as two layers in the body wall. Ex : Coelenterata.

 

2. Triploblastic animals - having ectoderm, mesoderm and endoderm as three layers in the body wall.

 

 

The Triploblastic animals are further divided into three groups based on the presence or absence of an embryonic body cavity called coelom.

 

1.  Acoelomata - no coelom Ex : Platyhelminthes

 

2.  Pseudocoelomata - with a false coelom Ex : Nematoda

 

3.  Coelomata - with a true coelom

 

IV. In a recent system, the entire living world is subdivided into 5 kingdoms. This system is much more broader including algae, fungi, and plants. It is known as the Five kingdom concept.

 

1.  Kingdom : Monera - It includes all bacteria and the cyanobacteria. A circular DNA occurs in the cytoplasm. The cell wall is a rigid structure. a) Phylum :Cyanobacteria b) Phylum : Bacteria.

 

2.  Kingdom : Protoctista or Protista - It includes single celled eukaryotes. It has two subkingdoms, namely Protozoa and Algae.

 

3.  Kingdom : Fungi

 

4.  Kingdom : Plantae (green plants)

 

5.  Kingdom : Animalia : multicellular, eukaryotic animals.

Comments

Post a Comment

Popular posts from this blog

Plasma Membrane

  Plasma Membrane   It is the outer limiting membrane of both prokaryotic and eukaryotic cells. It is an ultra thin, elastic, living membrane. Plasma membrane is a dy-namic and selective transport barrier.   Since the plasma membrane is ultra thin, it could be observed only under electron microscope. Structure of the membrane is studied by isolating the same from the cell and conducting biochemical investigations.   In 1895  Overton  suggested that the membrane is made of fatty sub-stances. Other workers later concluded that two layers of lipid were present in the cell membrane. According to a model proposed by  Danielli  and  Davson  in 1935, the  lipid bilayer  of the membrane was coated on either side with protein.   In 1960,  Robertson  using electronmicrographs proposed a  unit   membrane hypothesis . According to this hypothesis the two outer layers of  protein are about 2 nm thick and appear densely granular. They enclose a   clear central area of about 3.5 nm wide consisting of
Read more

THEORIES OF EVOLUTION : Neo-lamarckism

  THEORIES OF EVOLUTION   Neo-lamarckism   Lamarck's 'theory of inhertitance' was further studied by a group of scientists. Their ideas supporting Lamarck's opinion collectively constitute neo-Lamarckism.   The neo-Lamarckians were of the opinion that 'adaptions' are universal in nature. An adaptation happens through causal relationship of structure, function and environment. Due to changes in the environment, habits and life style of organism gets altered. Thus gradually the organism acquires new structures. The newly obtained character gradually becomes an inheritable trait. This opinion and argument is a modified form of Lamarckism. These ideas stressed direct action of environment on organisms.   Support to neo-Lamarckian concept - Experiments   1. McDougall (1938) tried to prove that learning is an acquired character that can be inherited. He did his experiments on rats.   He deviced a 'T' shaped tank. The tank had two exits. One exit was well light
Read more

History of Human anatomy

  History of Human anatomy   The term 'anatomy' is Greek in origin. It takes its root from 'ana' and 'tome' (ana-up ; tome-cutting). Thus anatomy is the science of physical structure of an animal or plant studied by dissection. The Human Anatomy provided the necessary knowledge for surgery and medicine.   The study of human anatomy dates back to 2500 BC, when the Egyptians prepared mummies. They removed internal organs of cadavers be-ing mummified. They also did surgery for wounds and broken bones. In India during 500 - 491 BC Susruta performed cataract operation. In 1 st  century AD, Celsus, a Roman physician wrote about surgical procedures.   The year 1543 AD was significant due to publication of an accurate book on Anatomy by Andreas Vesalius. In 1628 William Harvey described the functioning of heart and the movement of blood in animals. These earlier works were followed by the discovery and accurate account of each and every or-gan system and organs in human
Read more