Kingdom Animalia

1.0Cellular Nature 

Cells of members of kingdom animalia are wall less, eukaryotic and multicellular. It is heterotrophic. Most animals are mobile.

2.0Basic Terms Used

Body symmetry: It is symmetry in the arrangement of body parts.

Radial symmetry: The body can be divided into similar halves by any plane passing through the centre axis.

Bilateral symmetry: The body can be divided along a median longitudinal plane into two mirrored portions on the right and left halves.

Germ layers: They are the primary layers that differentiate in the embryo. All tissues and organs of the animal body develop from them. In animals either two or three germ layers are present.

Diploblastic animals: Having two germ layers i.e. ectoderm and endoderm.

Triploblastic animals: Having three germ layers i.e. ectoderm, endoderm and mesoderm.

Metameric segmentation: Body is divided into segments externally as well as internally (by septa). Segments are called metamers.

Body cavity [Coelom]: A body cavity having a fluid-filled space between the gut and the outer body wall of an animal.

Acoelomates: Animals without coelom e.g. Flatworms

Pseudocoelomates: In these animals, coelom is not lined by mesoderm. e.g. Nematodes.

True coelomates: In these animals, coelom is lined by mesoderm.

e.g. Chordata.

Body temperature

Ectotherm or Poikilotherm or cold-blooded organisms can change their body temperature according to environmental temperature. e.g. Pisces, Amphibians, Reptiles.

Endotherm or Homeotherm or warm-blooded organisms cannot change their body temperature according to environmental temperature. e.g. Aves and Mammals.

3.0Phylum Porifera

Organisms have holes or ‘pores’ all over the body. These pores are called ostia and they open into the canal system. The canal system opens to the outside by a single osculum.

The canal system helps in circulating water throughout the body to bring in food and oxygen.

These are non-motile animals attached to some solid support. These animals are covered with a hard outside layer or skeleton. They have cellular organization. They are commonly called sponges and are mainly found in marine habitats. e.g. Sycon (Scypha) - Urn sponge, Euplectella - Venus’s flower basket, Euspongia - bath sponge, Spongilla

4.0Phylum Cnidaria or Coelenterata

They are aquatic animals mostly marine, some of them live in colonies (corals) while others live solitary (hydra). The body is radially symmetrical and diploblastic.

These are the first multicellular animals having tissue level organization with distinct division of labour. The body has a central gastrovascular cavity - coelentron which lacks anus but has mouth which is surrounded by tentacles. 

The body of coelenterates bears specialized cells-cnidoblasts, bearing stinging cell organelles called ‘nematocysts’ which serve the function of paralysing the prey by injecting poison.

e.g. Hydra: fresh water coelenterate, Millepora-coral, Physalia-Portugese man of war, Aurelia -jelly-fish, Metridium- sea-anemone.

5.0Platyhelminthes (Flatworms)

They are mostly parasitic animals (e.g. liver flukes) but some are free-living (e.g. Planaria) and aquatic.

They show bilateral symmetry.

They are triploblastic animals which allow outside and inside body linings as well as some organs to be made and thus, tissue-organ grade of body organization is present. The organisms are unsegmented and dorsoventrally flattened.

Body cavity (coelom) is absent i.e. acoelomate.

Suckers and hooks are usually present.

In Platyhelminthes, the alimentary canal has only one opening (mouth) and anus is absent. They have blind tubules called protonephridia, having (flame cells) for excretion.

e.g. Planaria or Dugesia, Fasciola-Liver fluke, Taenia Solium - Pork tape worm.

6.0Phylum-Nematoda or Aschelminthes (Thread Worm or Round Worm)

They are parasitic worms causing diseases.

Most are free living (in fresh or marine water or terrestrial).

They have narrow, elongated and cylindrical bodies. The body is covered by cuticles.

Triploblastic unsegmented animals with bilateral symmetry and organ system level of organization, having tube within tube body plan.

Pseudocoelom is present.

e.g. Ascaris - round worm, Wuchereria - filarial worm causing elephantiasis.

Most of the members of nematoda show sexual dimorphism i.e. there is distinct difference in size or appearance between the sexes of animals in addition to the sexual organs themselves.

Male Ascaris are smaller than female Ascaris. The posterior end of male Ascaris is curved whereas the posterior end of female Ascaris is straight. Two pineal setae are present in male Ascaris but absent in female Ascaris.

7.0Phylum- Annelida (Segmented Worms)

They occur in fresh water, sea water or moist soil. Some are free living, some are burrowing and few are parasites. They are the first animals with true body cavity i.e. coelom.

They are bilaterally symmetrical, triploblastic animals. The body is covered by a thin cuticle.

The alimentary canal is complete. The blood vascular system is closed. Blood is red due to the presence of the pigment haemoglobin.

Blood in annelids is red due to the presence of haemoglobin. It is dissolved in plasma. R.B.Cs are absent.

e.g. Nereis - sand worm (clam worm), Aphrodite - sea mouse, Pheretima - Earthworm, Hirudinaria - Indian cattle leech.

8.0Phylum Arthropoda (The Animals with Jointed Feet)

The largest group of animals.

They are found everywhere on earth - on land, in soil, in water and as parasites on plants and other animals. 

Triploblastic, bilaterally symmetrical and metamerically segmented animals.

The body is segmented into 2 regions- head and thorax together and abdomen or 3 regions- head, thorax and abdomen. The anterior part of the body forms a distinct head, bearing sense organs. 

Animals have jointed legs (3 or more pasirs).

The body cavity is filled with blood i.e. haemocoel. An open circulatory system is present i.e., blood does not flow in well defined blood vessels.

Mouth parts adapted for biting, chewing, piercing and sucking. 

Respiration occurs through the general body surface, gills, tracheae or book lungs. Reproductive organs are present on the separate individuals. 

Arthropods have compound eyes. Exoskeleton is made of chitin. Excretion occurs by ‘Malpighian tubules’ or green glands or coxal glands.

Blood may be colourless - haemolymph (e.g. insects) or with copper containing pigment -haemocyanin (e.g. prawn).

e.g. Palaemon - Prawn, Cancer - crab, Scolopendra - Centipede, Julus - Millepede, Periplaneta-Cockroach, Musca - House fly, Apis - honey bee, Anopheles - mosquito, Palamnaeus- scorpion, Aranea - spider, butterflies.

 Differences Between Annelids and Arthropods

9.0Phylum Mollusca (The soft bodied animals).

The second largest group of animals. They are mostly aquatic, living in sea water and some are in fresh water. They are soft, unsegmented, triploblastic, coelomate animals with bilateral symmetry. Locomotion is brought about by muscular feet.

E.g. Chiton-Coat of mail shell, Pila-apple snail, Unio-fresh water mussel, Sepia-cuttle fish, Octopus- devil fish.

In phylum mollusca blood is usually blue due to a blue pigment called “haemocyanin”. They have an open blood vascular system and excretion occurs by a pair of kidneys or metanephridia, known as Kaber’s organ or Organ of Bojanus.

The body of mollusc is divided into an anterior head, a ventral muscular foot and a dorsal visceral mass of hump. Over the hump, a fold of thin skin called mantle or pallium is present, which secretes the shell. The soft body is usually supported by a hard shell of calcium carbonate.

10.0Phylum - Echinodermata (The spiny skinned animals)

They have hard calcium carbonate structures that they use as a skeleton.   

They are exclusively marine animals.

The body is triploblastic, coelomate and without segmentation with radial symmetry in adult and bilateral in larvae.

The body cavity is modified into a water vascular system. Tube like extensions called tube feet. Tube feet help in locomotion and food collection.

The digestive system is complete, the mouth is on the lower surface and the anus is on the upper surface.

Respiration takes place by gills, genital bursae or respiratory trees.

Reproduction sexual, asexual or by regeneration and sexes are separate.

E.g. Asterias - star fish or sea star, Ophioderma - brittle star, Echinus - sea urchin, Holothuria - sea cucumber, Antedon - feather star.

11.0Phylum - Hemichordata

Hemichordata was earlier considered as a sub-phylum under phylum Chordata. But now it is placed as a separate phylum under non-chordata.

This phylum consists of a small group of worm-like marine animals with organ-system level of organisation. They are bilaterally symmetrical, triploblastic and coelomate animals. The body is cylindrical and is composed of an anterior proboscis, a collar and a long trunk. The circulatory system is of open type. Respiration takes place through gills. The excretory organ is a proboscis gland. Sexes are separate. Fertilisation is external. Development is indirect. 

Examples: Balanoglossus.

12.0Phylum-Chordata 

Chordata is a phylum of triploblastic bilaterally symmetrical coelomate animals.

A notochord is a long rod-like structure that develops between the dorsal nervous system and gut. Notochord functions as a support structure that provides points for attachment to muscles. Dorsal hollow nerve cord occurs above the notochord. 

Sub-phylum Vertebrata has following important classes: