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1800-102-2727Have you visited any construction site in your neighbourhood? Can you guess what’s the first thing done before assembly of bricks and other construction work? It’s planning. Like the way every building has a plan, our body also has a plan. Amazingly, this plan is actually one of the bases of classification.
Like a train with repetitive compartments, certain creatures have compartments in their bodies which get repeated. The nature of compartmentalisation varies in our bodies just like in trains. Some trains have differently coloured and structured compartments while some have uniform. Similarly, the type of compartmentalisation in our body can be taken as a basis of classification.
You must have felt the vertebral column at the back? Have you ever investigated if an earthworm has a spiny structure at its back or not! That’s of biologists interest. How? So, the presence or absence of notochord is a basis of classification of animals.
Let’s dig holes into body plan, segmentation and notochord and understand how these are helping in the classification of animals.
The set of morphological features which are common to the organisms belonging to a particular phyla is collectively known as body plan.
Types of body plan |
Observation |
Possible category (members of phyla) |
Figures |
Cell aggregate type |
Cells are arranged as loose cell aggregates. |
Porifera (sponges) |
|
Blind sac type |
Incomplete digestive system where only a single external opening (blastopore) serves as both mouth and anus. |
Coelenterata, Ctenophora, Platyhelminthes |
|
Tube-within-a-tube type |
Alimentary canal extends from the mouth to anus inside the body. This appears like a tube within a tube, with fluid-filled cavities in between the two. |
Aschelminthes, Annelida, Arthopoda, Mollusca, Echinodermata and Chordata |
|
The divisibility of the body into similar constituent units is termed as segmentation.
Types of animals |
Nature of segmentation |
Possible category (members of phyla) |
Figures |
No segmentation |
Body is not divided into segments. |
Porifera, Coelenterata etc. |
|
Pseudo metamerism |
Body is externally divided into segments but it is not coherent with internal segmentation. |
Platyhelminthes |
|
Metamerism |
Body is externally and internally divided into segments with serial repetition of organs in the segments and a coordination between them to attain a specific function. The body segments are called metameres. |
Annelida, Arthopoda and Chordata |
|
Notochord is defined as a rod-like structure derived from the mesoderm during the development of the embryo. It is present on the dorsal side of the animal body.
Types of animals |
Presence or absence of notochord |
Possible category (members of phyla) |
Non-chordate |
Animal without a notochord. |
Porifera to Hemichordata |
Chordate |
Animal with a notochord. |
Chordata |
Ques:- “I am ‘Spongey’. I have a cell aggregate type body plan. Can you help me find my phyla?”
A. Coelenterata
B. Ctenophora
C. Porifera
D. Echinodermata
Solution: The organisms which have cells arranged as loose cell aggregates are said to have cell aggregate type body plan. Members of phylum Porifera have a cell aggregate type of body plan.
Hence, the correct option is c.
Ques:- Bodies of tapeworms are externally divided into many segments. How are they different from annelids which also show external segmentation?
A. Tapeworms show metamerism which is absent in annelids
B. Tapeworms show external segmentation while annelids exhibit metamerism
C. Tapeworms show internal segmentation which is absent in annelids
D. Tapeworms show external segmentation while annelids show only internal segmentation
Solution: Tapeworms have their bodies externally divided into several repeating segments. This is also called pseudometamerism. Annelids exhibit true metamerism with bodies having segments with external and internal partitions.
Hence, the correct option is b.
Ques:- An organism has an organ system level of body organisation but shows radial symmetry like ctenophores. Predict the phyla under which it falls.
A. Coelenterata
B. Platyhelminthes
C. Echinodermata
D. Chordata
Solution: Members of phylum Echinodermata have organ system level of body organisation. Adult echinoderms can be divided into two equal halves across multiple planes passing through the central body axis.
Hence, the correct option is c.
Ques:- Which of the following body plans is found in organisms having an organ system level of body organisation?
A. Cell aggregate type
B. Tube-within-a-tube
C. Blind sac
D. Either a or c
Solution: Organisms having organ system level of body organisation can be members of phylum Aschelminthes/ Annelida/ Arthopoda/ Mollusca/ Echinodermata or Chordata. These members have alimentary canals extending from the mouth to anus inside the body giving the appearance of a tube lying within another tube.
Hence, the correct option is b.
Ques:- Define metamerism.
Solution: Segmentation in which there is recurrence of certain organs in each segment is known as metamerism. Besides, the external segmentation coincides with internal segmentation. It is also known as true segmentation. Example: Members of the phylum Annelida.
Ques:- Name the fundamental feature(s) used to classify the animals.
Solution: List of fundamental feature(s) used to broadly classify the animal kingdom are as follows:
Ques:-Name the phylum that has a cell aggregate body plan.
Solution: Cells are arranged as loose cell aggregates in a cell aggregate body plan. It is found in the members of phylum Porifera.
Ques:- Define notochord along with its functions.
Solution: Notochord is a mesodermally derived rod-like structure which is formed on the dorsal surface of the body during embryonic development in some animals. Animals having notochord are termed chordates.
The notochord gives rise to the vertebral column in vertebrates. It provides protection to the spinal cord.