Animal Classification

Features that are used for Identification and classification of animals.

It can be according to the

Number of cell and nature of nucleus - First we have to identify number of cell- unicellular (single cell) or multicellular (more than one cell). Nature of nuclease prokaryotic(membrane bound nucleus is absent) or eukaryotic (membrane bound well developed nucleus is present).

Body symmetry - Body can be asymmetric (no matter how it be cut but two halves will be never symmetrical, examples-amoeba), radially symmetrical (any line passing through the center will divide the body into two similar halves,example-starfish), bilateral symmetry (almost all the vertebrates and the large number of invertebrates, examples – human).

Arrangement of cells – In lower animals cells of their body are not so compact. As the phylum porifera contains many holes in their body as water circulation is observed in their body. On the other hand body of higher animals contains compact cellular layer – produce dermis.

Presence of coelom – In lower animals coelom is absent. Platyhelminthes are acoelomate, where as nematohelminthes are pseudocoelomate ,and true coelom is appeared first in annelids. As three layers of skin is observed ectoderm,mesoderm, endoderm (from outside to inward).

Body segment – Some animals are there whose body is divided into inner and outer segment. Example earth worm body is segmented into both outer and inner way. This are called metamear.

Embryonic development – Embryology is the study of early development of an individual from zygote to young ones. Different parts are developed from specific part and specific time of gastrulation.

Presence of notochord – If the specimen carry notochord in any stages of their life or throughout their life is termed as notochord.

Type of different system like circulatory system, digestive system, excretory system:

Circulatory system - In lower animals there are open circulatory system that means blood is pumped out from the heart directly into different parts as there is no blood vessels to carry the blood. In higher animals there are blood vessels (artery, veins, capillaries) to carry blood .In some extreme lower animals water is act as the circulatory material.

Heart – Presence of number of chamber in heart. From lower to higher number of chambers are are increased. In fish there are two chambers , in amphibian they have three chambered heart, in reptiles they have incomplete four chamber heart, in birds and mammals they have complete four chamber heart.Birds and mammals are warm blooded (their body temperature remain unchanged with the change of temperature) animals and the rest are cold blooded (body temperature changes with the temperature). In fish mixed blood is carried, in amphibian pure and impure blood carries separately but they mixed after sometime. But in case of birds and mammals pure and impure blood never mixed.

Kidney – Some of them are pronephros, mesonephros, metanephros.

Brain – It has been observed that cerebrum is bigger in higher animals which is responsible for memory, thinking, intelligence etc than lower animals.

Classification of animals -  By finding the similarities and dissimilarities with other animals new specimen can be categorised into respective species, genus, family, order, class, phylum, Kingdom.

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