Characteristics of different classes of phylum chordata
Do you know what are the different classes of phylum chordata? In this article you will find the characteristics of different classes of phylum chordata. To know the characteristics of different classes of phylum chordata, please read this article.
According to five kingdom classifications , animal kingdom is divided into two sub kingdoms; non chordata and chordate. The characteristics of non chordates are described in my two articles, characteristics of different phyla of kingdom animalia part I and Part II . In this article I will explain the characteristics of different classes of chordata.
Characteristics of chordata
Chordata is the most advanced and largest phylum of animals. This phylum was established by Balfour (1880). All the animals are characterized by presence of cord like structure called Notochord which is found in larval or embryonic stage or throughout the life cycle. About 50,000 living and 25,000 extinct animals of this phylum have been identified till date. The general characteristics of phylum chordata are:
- Chordates are distinctive in having a notochord, dorsal hollow nerve cord and paired gill slits on the sides of the pharynx.
- The notochord is a dorsal longitudinal rod composed of a fibrous sheath enclosing vacuolated cells.
- Chordates possess notochord either throughout whole life or during early embryonic period.
- The nerve cord is dorsal to notochord and differs from that if invertebrates not only in position but also in structure it is a single hollow tube.
- The gill slits remain functional only in gill breathing animals. In higher lung breathing forms, it disappears during later development. In the members of sub phylum vertebrata the notochord is present only during embryonic period.
- A series of vertebrae soon surround it and the dorsal nerve cord. This is known as vertebral column of backbone.
- There are certain lower chordates which do not develop a true backbone or vertebral column. These are known as protochordates. These are exclusively marine forms. E. g., in Amphioxus the notochord and the nerve cord extends the entire lenghth of the adult. Their body is laterally compressed and leaf like.
- Closed circulatory system is found.
- Postanal tail is found.
Characteristics of Pisces
The main characteristics of Pisces are:
- The animal of Pisces are aquatic.
- Body of these animals are covered by scales.
- Body is streamlined to swim in water.
- Respiration takes place by means of gills.
- Heart is two chambered. It is called venous heart.
- Animals have paired pectoral and pelvic fins. Besides, two dorsal fins are also present. All the fins help in swimming.
- Animals are cold blooded, i, e., Poikilothermic.
Characteristics of amphibia
Most amphibians have two phases of their life. In their first phase or larvae stage they are fishlike aquatic forms, but in the adult phase, they move about on land with four limbs and respire by means of lungs and skin. For breeding they return to water. Eggs and sperms are laid in water and the fertilized egg develops into tadpole larva. The general characteristics of amphibians are:
- Amphibians can live both on land and in water.
- Body is divided into head, trunk and tail.
- Adult amphibians are tetrapods with two pairs of limbs. Fore and hind limbs have four and five digits respectively. Hind limbs are usually longer which help in jumping and swimming.
- Skin is soft, slimy and naked.
- Exoskeleton and scales are absent.
- Skin also serves as an accessory respiratory organ.
- In some animals, poison glands may be present in skin. Chromatophores or pigment glands are also present.
- Endoskeleton is bony. Skull is dicondylic.
- Eyes are provided with movable eyelids.
- Ear consists of an outer membrane known as tympanum. It is stretched over auditory canal. An ear bone, columella auris conducts sound vibrations in the membrane to the fluid filled sensory inner ear.
- Respiration takes place by means of gills, lungs, skin or buccal cavity. Gills are generally found in larval forms but it persists in some amphibians to adult stage also.
- Heart is three chambered two auricles and one ventricle. R.B.Cs. are nucleated. In tadpole stage, the heart is two chambered.
- Kidney is mesonephric and uricotelic.
- Cranial nerves are 10 in numbers.
- Animals are cold blooded, i, e, poikilothermic.
- Amphibians are unisexual, fertilization is external and oviparous.
- Development is indirect. Cleavage is unequal and holoblastic.
Common examples of amphibians are Rana (frog), Bufo (toad), Hyla (tree frog), Alytes (midwife toad), Pipa (Surinam toad), Ichthyophis, Salamander, Rhacophorus, etc.
Characteristics of reptilia
Reptilians are cold blooded vertebrates with elongate low stature body. Reptilians are usually seen creeping or crawling on the ground. Class reptilian has more extinct than living species. Reptilians are true landforms and need not return to water to reproduce. There are about 6,000 species of reptiles living now. Reptilia include lizards and snakes, turtles and tortoises and the crocodiles and alligators. The general characteristics of reptilians are:
- Reptilians are first fully terrestrial animals with dry, horny, scaly and impervious skin. Snakes and lizards shed their scales as skin cast. Scales help to prevent to loss of water.
- Limbs pentadactyl, each limb with five digits ending into claws.
- Respiration takes place only with the help of lungs. Gills are absent.
- Heart is three chambered. But it is further improved through the partial division of ventricle by a septum. Thus, the oxygenated blood from the lungs is not completely mixed with the deoxygenated from the rest of the body. In crocodiles, the heart is four chambered as in birds and mammals.
- Reptilians are cold blooded animals.
- Reptilian are mostly terrestrial but some are aquatic.
- R.B.Cs. are nucleated.
- Internal fertilization occurs in reptilians.
- Reptilians are generally oviparous. A few snakes are viviparous.
- Body can be divided into head, trunk and tail.
- Sexes are separates.
Characteristics of aves
The members of class aves are characterized by the presence of feathers and power of flight. About 9,000 species of birds are known to us. The general characteristics of aves are:
- Body is streamlined and divided into head, trunk and tail. The long tail helps is balancing the body.
- Body is covered with feathers.
- Projecting ear is absent. At its place a pore leads to the ear drum.
- Forelimbs are modified into wings. Hind limbs are adapted for perching, walking and swimming.
- Feathers form the exoskeleton. Scales are usually absent. Sometimes, these may be present on legs.
- Bones are pneumatic or porous. It reduces the weight and helps in flying.
- Powerful flights or breast muscles helps in flying. These are attached to a large breast bone.
- Horny beak is present in head. Teeth are absent. Beak is modified according to feeding habit.
- Respiration takes place by means of lungs which are provided with thin walled air sacs. Voice box called syrnix is present.
- Heart is four chambered. It beats fast and pumps large amount of blood into the body. R.B.Cs. are nucleated.
- Kidney is metanephric and trilobed. Ureters open into cloaca. Urinary bladder is absent.
- Nervous system well developed. These are 12 paris of cranial nerves.
- Eye balls are well developed. It helps in searching the food and shelter from a height while flying.
- Aves are oviparous. Eggs are incubated by parents via constant body temperature.
Characteristics of mammalia
Mammals are the most successful and dominant animals today. Class mammalia contains about 4,000 species of mammals living in all mountains, forests, grasslands and dark caves. The general characteristics of mammalians are:
- Body usually covered with hairs which might occur all over the body or restricted to particular areas.
- Skin thick and water proof with sweat glands and sebaceous glands. The females are provided with milk producing mammary glands to nourish the young ones. In males they become vestigial.
- Ear with fleshy external ear or pinna.
- A muscular diaphragm is present which separates the thoracic cavity from the abdominal cavity.
- Teeth are the codont, heterodont and diphyodont.
- The heart is four chambered with two auricles and two ventricles. Only the left aortic arch is present.
- Respiratory system is well developed. Pulmonary breathing is enhanced by the muscular diaphragm which separates the thoracic cavity from the abdomen. Constant up and down movements of diaphragm increases the air intake in the lungs.
- The mammals have well developed brain, this enables them to learn. To a great extent the instinctive behaviour is replaced by the learned behaviour in mammals.
- Lower jaw formed of a single dentary bone of each side.
- Cervical vertebrae are always seven in number.
- Mammals are warm blooded.
- Mammals are mostly viviparous. The embryo is attached to the uterine wall by placenta. They exhibit parental care.
So, dear friends, these are the characteristics of different classes of phylum chordata.