Question

Write short notes on :
(a) Coelom (b) Metamerism (c) Notochord

Answer 1

Hint: There are fundamental features common to various individuals in relation to arrangement of cells, body symmetry, nature of coelom, patterns of digestive system, circulatory system and respiratory system

Complete step by step answer:
COELOM: .Presence or absence of cavity between the body wall and the gut wall, the body cavity lined by mesoderm is known as coelom.
Acoelomates : animals which do not possess cavity or coelom in the digestive tract. Eg. Platyhelminthes.

Coelomates : animals possessing coelom between the body wall and the digestive tract are called coelomates.eg. annelids, arthropoda etc.

Pseudocoelomates: in some animals the body cavity is not lined by mesoderm instead the mesoderm is present in the cavity in between the ectoderm and endoderm. Eg. Aschelminthes.

METAMERISM:
Metamerism or segmentation refers to a linear repetition in parts in the animal body.
Each segment is called metamere or somite.
Segmentation often affects both external and internal structures. Such a condition is called metameric segmentation. Eg. Annelida, Arthropods and Chordates

NOTOCHORD:
The notochord is a solid, unjointed, stiff but flexible rod located in the mid dorsal line between the alimentary canal and the nerves cord of embryo.
Notochord provides support and points for muscle attachment
It persists throughout life in the lower chordates but in the higher ones it is surrounded or replaced partly or fully in the adult by a jointed vertebral column or backbone.
There is no notochord in non chordates.

Additional information:
The fluid in coelom is called coelomic fluid., acts as a simple circulatory system , transporting food, gases and wastes around the body. Further they give space for development of a true circulatory system.
In the adult chordates, segmentation is visible in the internal structures such as vertebrae, ribs, nerves and blood vessels.
Animals with notochord is known as chordates and without is known as non chordates

Note:
 The nature of coelom, metamerism and notochord forms the basis of classification in the animal kingdom.