The kingdom animal consists of multi cellular eukaryotic organisms. It consists of many phyla which are mentioned below.
Phylum Porifera are pore bearing animals. Phylum Cnidaria has stinging cells and coelenterons with single opening. Flatworms come under Phylum Platyhelminths. Round worms and segmented worms are included under Phylum Nematoda and Annelida respectively. Animals with jointed feet are included under Phylum Arthropoda. The soft body animals and spiny skinned animals are included under Phylum Mollusca and Phylum Echinodermata. Hemichordata and Chordata Phylum include stomochord which are hollow structures organisms and the organisms with notochord are solid and rod like. The subphyla included are urochordata, cephalochordata and vertebrata. In urochordata the notochord are present in the posterior part of body. The cephalochordate includes the animals with notochord in the anterior part of body also. Vertebrata includes the animals where notochord is replaced by vertebral column. They are further divided as jawless and jaw vertebrates. They are known as agnatha and gnathostomata respectively. They also include Pisces which are true fishes. They are further divided into placodermi which includes extinct fishes.
Chondrichthyes includes cartilaginous fishes and bony fishes are placed under Osteichthyes. Tetrapoda are the animals with 4 limbs. This super class includes amphibian, reptilian, aves and mammalia. Amphibia are the animals with double mode of life. Reptilia are creeping vertebrates and Aves include birds. Mammalia includes mammals. The animals which belong from Phylum Porifera to Hemichordata are known as non chordates as they do not have notochord. The rest of the animals which belong to non chordates, urochordates and cephalochordates are known as invertebrates as they do not have vertebral column.
How can Animals be classified ?
Animals can be classified on the basis of habitat, habits, levels of organization, body plans, symmetry and segmentation etc.
How can Animals be classified on the basis of habitat?
On the basis of habitat these are classified as aquatic and terrestrial animals. Aquatic animals are further divided as zooplankton, nekton and benthos. They live in water which may be classified as sea water (marine) or fresh water. Terrestrial animals are further divided as cursorial, arboreal, aerial and fossorial. Zooplanktons are the animals in body of water which are floating. Nektons are actively swimming animals in the body of water. Benthos constitutes animals which occur at the bottom of water body. Terrestrial animals live on land. Cursorial animals run fast and arboreal animals live on tress. Aerial animals can fly and fossorial live in burrows.
On the basis of habit they can be classified as discrete, solitary, colonial, gregarious, motile etc. Solitary animals are those organisms which live alone. Some of them also live in groups and are known as colonial animals. They do help one another. Gregarious animals live in groups and do not help each other. There are free living animals which live independent life while some of them are parasites which depend on other animals for their survival. Some animals can move and are known as Motile animals. Sessile animals are fixed to the substratum. A few animals feed on blood, fecal matter and organic matter. These animals are known as sanguivorous, coprophagous and saprophagous respectively.
There are certain aspects of habit which are mimicry, autotomy, regeneration, hibernation and aestivation. Mimicry is the similarity of one organism to the other organism or object for protection. Autotomy means self injuring the part of own body. Regeneration means regaining the lost part of body from small part of organism body. Hibernation and Aestivation are referred as winter and summer sleep respectively.
On the basis of level of organization animals can be classified as cellular, tissue and organ level. At cellular level the body of animals is made up of cells which may be similar or not. The tissue level consists of poorly defined tissue organisms and is multi cellular. In the organ system of classification cells form organs. Most of the animals of kingdom animalia are included in the organ system of classification.
Depending upon the body plan animals are classified as cell aggregate, blind sac and tube within a tube. In cell aggregate plan the animals have cluster of cells which are not organized to form tissues. In Blind sac plan the animals have single opening which serves the purpose of ingestion and egestion. Tube within a tube plan consists of couple of tubes. One forms the body wall and other forms digestive tract. Digestive tract has mouth and anus. Tube within a tube plan is divided as protostomic and deuterostomic. In protostomic animals mouth is developed first and the anus is formed later on. These animals are known as Protostomes. In deuterostomic animals anus is formed first and mouth of the digestive tract is formed later on. These types of animals are known as deuterostomes.
How can Animals be classified on the basis of body plans?
On the basis of body symmetry the animals are classified as spherical, radial and bilateral symmetrical. A body is defined as symmetrical when it can be divided into two equal halves by any plane. A body is defined as asymmetrical when it cannot be divided into two equal halves by any plane. In spherical symmetry body can be divided into two equal halves by a plane passing through centre. They are of spherical shape. In radial symmetry body can be divided into two equal halves by a plane passing through centre from top to bottom. They are of radiating shape. When the division occurs by one or two vertical planes it is called bi radial symmetry. In this the animals show oral and aboral side. The oral side corresponds to the mouth and aboral is opposite to oral side. In bilateral symmetry body can be divided into two equal halves by a single plane. It is found in invertebrates and vertebrates. They form lateral sides which correspond to the right and left sides. There is anterior side which is kept forward and a posterior side which is opposite to anterior side. Dorsal side is formed by the upper surface and under surface is formed by ventral side. There are also proximal and distal end. Proximal end corresponds to the tissues and organs which are adjacent to the point of attachment. Distal end corresponds to the tissues and organs which are away from the point of attachment.
Depending on the planes animals are classified as transverse plan and horizontal plane. A plane which passes at 90 degree to the longitudinal axis is known as Transverse plane and a cut in this plane is known as Transverse section. A plane which goes longitudinal through anterior to posterior end is called Horizontal plane and a cut in this plane is known as Horizontal section. A plane which goes dorso ventrally extending through the length of body is called Vertical plane. A cut in this plane corresponds to Vertical section.
Germ layers are primary layers of cell which differentiate in the embryo at the gastrulation stage and give rise to all the tissue and organs of an individual. Some of the animals like porifers and coelenterates are made up of two germ layers such as ectoderm and endoderm respectively. These are known as diploblastic animals. While a most of them are formed from ectoderm, mesoderm and endoderm. These are known as triploblastic animals.
Segmentation in the animals can be true or false. True segmentation is also known as metameric segmentation. While false segmentation is known as pseudo metamerism. In true segmentation the body is divided externally and internally into segments. It includes annelids, arthropods and chordates. In pseudo metamerism there is no such division of external and internal segments. It includes tapeworms.
A distinct head formed at the anterior end is known as cephalization. The creeping habit of animals played a vital role in the evolution of cephalization. There are appendages which are projected from the body and serve the purpose of locomotion, feeding etc. It includes legs, fins, antennae, foots and parapodia. Animals can be warm blooded or cold blooded depending on the surrounding temperature. Warm blooded are also known as endothermic and cold blooded are also known as ectothermic. The ability of the animals to change their body temperature according to surroundings is known as ectothermic phenomena. The inability of the animals to change their body temperature according to surroundings is known as endothermic phenomena.
When both the sex organs that are male and female are present in an individual it is known as hermaphrodite. It includes tapeworm, earthworm and leech etc. The animals having one sex organ are known as unisexual. It includes frog, lizard and rabbit etc. In sexual dimorphism male and female animals can be differentiated externally. It is observed in peacocks and peahen, lion and lioness etc. There is a condition where the male reproductive organs mature earlier as compared with the female reproductive system and this is known as Protandry. There is a condition where the female reproductive organs mature earlier as compared with the male reproductive system and this is known as protogyny.
The union of gametes leads to fertilization. Gametes may be male or female type. Male gametes are sperms which are motile and female gametes are ova which are non motile. When the fertilization takes place outside the body of female it is known as external fertilization. It includes frog and starfish. When the fertilization takes place inside the body of female it is known as internal fertilization. It includes reptiles, birds and mammals. In self fertilization there is fusion of the gametes of same parent. Tapeworms are included in this group. In cross fertilization there is fusion of the gametes of different parents. Reptiles, birds and mammals are included in this group. Some animals lay eggs and are known as Oviparous. It includes birds and egg laying mammals. There are some animals which give birth to young ones and are classified as ovoviviparous and viviparous. The ovoviviparous animals give birth to off springs without formation of placenta. The off springs develop inside the eggs. It includes snakes and sharks. The viviparous animals give birth to off springs with the formation of placenta. It includes most of the mammals.
Development means changes the organism develops from its birth to maturity. It can be direct or indirect. In direct development the off springs resemble adults in all aspects excluding color and size. They do not have any intermediate stage. Star fish is an example of direct development. In indirect development the off springs do not resemble adults. They have an intermediate stage. Some of the animals have different stages of juvenile before they become adult and this process is known as Metamorphosis. Silk moth exhibits the process of metamorphosis.
The animals which do not have coelom are known as acoelomates. It includes sponges, flat worms etc. There are animals which have their cavity derived from blastocoels and are known as pseudocoel. It includes round worms. There are animals which have true coelom and are known as Eucoelomates. Coelom is derived from mesoderm which gives rise to lining known as coelomic epithelium. This epithelium forms coelomic fluid. Annelids, chordates and echinoderms possess a true coelom. It is sub divided as schizocoelom and enterocoelom. Schizocoelom are formed from mesoderm and includes annelids, arthropods and molluscs. Enterocoelom also arise from mesoderm from the wall of gut in the form of pouches. It includes echinoderms and chordates. Sometimes the coelom contains blood and is known as haemocoel. They occur in molluscs and arthropods.
