Animal Kingdom

May 11, 2023, 16:45 IST

Are you still looking for concise concepts related to Animal kingdom, then you have landed on the right page. The aim of the present article is to clear all your concepts related to the animal kingdom in a simple and engaging way.

First we will study the general characteristics of animals that include body symmetry, segmentation, circulatory system, digestive system etc. Then we will study how these characteristics classified the animals in different phylums. Once phylums are differentiated then we will study the specific characteristics that differentiate them from other phylums.

Table of Content
Introduction Characteristics of Animals Kingdom Phylums of Animal Kingdom Animals Kingdom FAQs

Introduction

Do you know, the utensils in your kitchen have some relationship with the animal species in the animal kingdom? The answer is as all varieties of utensils (plates, bowl and spoons etc.) make a kitchen in the same way different animal species with different characteristics together form animal kingdom. These characteristics may be their different body segmentation, notochord, circulatory system, respiratory system, body symmetry etc.

Let’s study characteristics one by one.

Characteristics of Animals Kingdom

Few of the characteristics are as follows:

Arrangement of cells

Cellular level - Cells are loosely arranged. Example- Sponges.
Tissue Level - Cells that perform the same function are organised into tissues. Example- coelenterates
Organ level - Tissues are grouped together to form organs, each specialised for a particular function. For example-Annelids, Arthropods, Molluscs etc.
Organ System Level - Different organs organised into organ systems. For example- Aschelminthes to Chordates.

Body symmetry

Asymmetrical - Any plane that passes through the center does not divide them into equal halves. Example- sponges.
Symmetrical - Body is divided into equal halves by one or more plane. For example-Hydra, Echinoderms etc.
Radial symmetry - Body can be divided into equal halves by any plane passing through the centre from top to bottom. eg., Hydra and jellyfish.
In Biradial symmetry the body can be cut into two similar halves by one or two vertical planes only, eg., Sea anemones and sea walnuts.
Bilateral symmetry - The body can be divided into two similar halves by a single plane. Example-Animalia

Embryonic layers

Three embryonic layers are ectoderm, endoderm and mesoderm which give rise to different organ parts.

Diploblastic animals - (two germ layers) ectoderm and endoderm, eg. porifera and cnidaria.
Triploblastic animals - (three germ layers)- ectoderm, endoderm and mesoderm, eg. platyhelminthes to chordates.

Coelom

Coelom is the internal body cavity that separates the digestive tract from the outer body wall. Types of coelom are:

Acoelom - No coelom eg. porifera, coelenterata, platyhelminthes (flatworms).
Pseudocoelom - Coelom is present but not lined by mesoderm, eg. roundworms, rotifers etc.
True coelom - Coelom is lined by mesoderm. eg. higher invertebrates.

SEGMENTATION

Body is divided into different portions and each portion is called segment/metamere with a serial repetition of at least some organs. For example-earthworm.

NOTOCHORD

Notochord is an elastic skeletal rod lying lengthwise beneath the nerve cord and above the alimentary canal in the embryos or adults of all chordate animals. It is found in both adult and larval lancelets but in adult vertebrates it is largely replaced by the vertebral column. e.g., porifera to echinodermata.

DIGESTIVE SYSTEM

Incomplete - single opening serves as both mouth and anus. Example-platyhelminthes.
Complete - Two openings, mouth and anus. For example-humans.

Circulatory system

Open - Blood is pumped out of the heart and the cells and tissues are directly bathed in it. There are no vessels. For example-Arthropods and molluscs.
Closed - Blood is circulated through a series of closed vessels of varying diameters (arteries, veins and capillaries). Example-many annelids and most chordates.

These were all the general characteristics that were used to classify animal kingdom into different phylums.

Phylums of Animal Kingdom

Let’s study characteristics in phylum in the form of a table.

Phylum	Level of organization	Coelom	Segmentation	Circulatory system	Digestive system	Respiratory system	Symmetry	Specific characteristics
Porifera	Cellular	Absent	Absent	Absent	Absent	Absent	Multiple	Body consists of canal system
Coelenterata (Cnidaria)	Tissue	Absent	Absent	Absent	Incomplete	Absent	Radial	Cnidoblast present
Ctenophora	Tissue	Absent	Absent	Absent	Incomplete	Absent	Radial	Locomotion by comb plates
Platyhelminthes	Organ and organ system	Absent	Absent	Absent	Incomplete	Absent	Bilateral	Flat body, suckers
Aschelminthes	Organ system	Pseudocoelomate	Absent	Absent	Complete	Absent	Bilateral	Elongated body
Annelida	Organ system	Coelomate	Present	Present	complete	Absent	Bilateral	Ring shape segmentation
Arthropoda	Organ system	Coelomate	Present	Present	complete	Present	Bilateral	Cuticle present, jointed appendages
Mollusca	Organ system	Coelomate	Absent	Present	complete	Present	Bilateral	External skeleton of shell is present, radula is present.
Echinodermata	Organ system	Coelomate	Absent	Present	complete	Present	Radial	Water vascular system
Hemichordata	Organ system	Coelomate	Absent	Present	complete	Present	Bilateral	Body is divided into proboscis, collar and trunk
Chordata	Organ system	Coelomate	Present	Present	complete	Present	Bilateral	Notochord, dorsal hollow nerve cord, gill slits with limbs and fins.

Animals Kingdom FAQs

Q1. What are cnidoblasts?

Ans. Cnidoblasts (stinging capsules) are cells present on the tentacles of an organism. They help them in defense, anchorage and capture of prey. For example-Physalia, Adamsia etc.

Q2. What are comb plates?

Ans. Comb plates are ciliated rows present in the body of ctenophores that helps in locomotion. Example-Pleurobrachia and Ctenoplana etc.

Q3. Which is the second largest phylum in the Animal kingdom?

Ans. Mollusca

Q4. What is the canal system in Porifera?

Ans. Canal system is present in sponges (Porifera) that help in transport of water. Water enters through small pores called ostia and exits out through the osculum.

Q5. What is radula?

Ans. The mouth of molluscs consists of file-like rasping organs for feeding called radula./p>