Information About Chordates


What are the properties, characteristics of chordates? Information on classes of chordates, non vertebrates and vertebrates.



Chordates are animals that have, at least at some time of their lives, a structure called a notochord. The notochord is a flexible, long supporting structure that runs through the body just below the nerve cord. Most chordates have a notochord when they are embryos. They also possess gill slits in some part of their life time.

Properties Of Chordates

• More or less developed, they have an endoskeleton (internal skeleton). The notochord is aligned on dorsal side of their body. Notochord remains for the entire life of the individual in some species, whereas some only have it in their embryonic stage. In some, notochord turns in spine.

• The neural tube located in the front of notochord expands towards the head and forms the brain; and the rest of neural tube turns into the spinal cord. Nerves extending from both the brain and the spinal cord form a network of nerve system throughout the body.

• Digestive system is located in the front of notochord, and in the front of digestive canal, respiratory system takes place. For aquatic organisms, the respiratory system includes gills; and for terrestrial individuals, the lungs.

• They have a closed circulatory systemi

Chordates are classified into two major groups:

Non- vertebrates

There are two subphyla of non- vertebrates. These are uro-chordates (tunicates) and cephalochordates (lancelets).

Tunicates are filter- feeding animals. All live in the seas. Some are solitaire and motile, whereas some sessile forms attach themselves to a point after larval stage. There are forms that live as colonies.

Lancelets are small marine animals. The most common example species of this group is Amphioxus lanceolatum, or, amphioxus shortly. Its body resembles a fish, but it is pointed at each end and is streamlined. Although it can swim, it generally lives partly buried in soil. It feeds on organisms in water drawn into its mouth.


The vertebrates are the most numerous and complex chordates. In vertebrates, the notochord is replaced by a bony or cartilaginous structure called the “vertebrae”, or with the common name backbone or spine.

Properties of Vertebrates

• Their body is covered with multi- layered epithelial tissue.

• They have a jointed endoskeleton. All vertebrates have a cartilaginous endoskeleton in embryonic period. In primitive forms, the cartilaginous skeleton remains for the rest of their lives; whereas in highly developed ones it turns into a bony structure.

• They have two pairs of extremities. The anatomical structure of these changes due to the job that they have. Marine vertebrates have fins; terrestrial ones have legs and arms. The muscles connected to the skeleton provide movement.

• The digestive canal starts with the mouth, and ends with the anus. Accessory glands that help digestion such as the liver and the pancreas are seen.

• All have a closed circulatory system. They all have hemoglobin for the transport of oxygen. They have chambered hearts.

• Their excretory organ is kidney.

• They have accessory structures formed by the skin such as glands, scales, feathers, hairs, nails, claws, horns and hoofs.

The vertebrates are classified into two major and six minor groups:

Agnatha (Jawless Fish)

Jawless fishes are the simplest vertebrates. They have a circular, sucking mouth, a tongue covered with teeth, a shortened permanent notochord, and an internal skeleton made of cartilage. Their heart is two chambered. The well known examples of this group are lampreys, hagfish and slime eels.


Fishes are aquatic vertebrates; most fishes have paired fins, scales and gills. On the basis of the components of skeleton throughout their lifetime, they are classified into two major groups.

Cartilaginous fishes possess internal skeleton of cartilage, mouth with true jaws, two pairs of fins, a skin covered with ting scales that have the same structure as teeth, and five pairs of slit like openings that lead into gill chambers. They respire by means of gills. They have a two chambered heart. They are cold- blooded animals. The well known examples are sharks, skates, and rays.

Bony fishes possess an internal skeleton of bone, skin covered with overlapping bony scales, a mouth with true jaws and swim bladders. They have spindle- like bodies with two chambered heart. Their gills are protected externally by a plate called “operculum”. Salmon, sea dragon and eels are the examples of this group.


The term “amphibian” means double life. As you all know, life has evolved from water to the land. Living on land, when compared to life in water is very risky. First of all there’s a great risk of not finding enough water most of the time. There’s also a risk of temperature, recall, which is very important for enzyme activity. So, it’ll be pretty easy to say that terrestrial animals should have some adaptations that will let them live on land.


Amphibians are not only land animals, nor only aquatic organisms. They have to be in water at least at their embryonic stage, and later, they have to “visit” their aquatic habitats frequently. The reason for this situation is that they are obligate to water for reproduction. Their eggs are not covered with a protective layer in order to prevent water loss, so eggs should be left in water. Moreover, they do not have adaptations which will prevent water loss throughout their skin, so they have to live near to water in order to dive down when necessary.

As to talk about their body plan and anatomical features, Ifeey have paired limps instead of paired fins; they have sensory organs developed for both aquatic and terrestrial life< When it comes to their respiration, it’s a bit complicated! They respire by their gills at larval stage. When they mature and are ready for life on land, a pair of lungs develops within the chest cavly, but these lungs are so primitiwthat they do not provide enough gas exchange for their metabolism, so they also use their skin for respiration.

This is one of the reasons why they have a slippery skin and they are very hard to hold in your palms! For diffusion of gasef, moist medium is required. If the skin of a frog dries out, it becomes very hard for them to properly exchange gases with the environment. They have a three chambered heart in which oxygenated and deoxygenated blood mixes. They are cold- blooded animals.

There are two major groups of amphibians. The tailed amphibians are called salamanders and nets; and the tailed amphibians are called the frogs and the toads.


Reptiles are animals that have fully adapted to life on land. Their skin is dry, includes no sweat glands, and is covered with keratin scales and plaques. They have two pairs of extremities with five fingers on each. In exception to this, in snakes and some lizards, the extremities have disintegrated in evolutionary process. They are the first vertebrates ever whose internal organs are protected wifi a ribcage. Their lungs and heart are relatively more developed when compared to amphibians. They have a three chambered heart with the exception of crocodiles and alligators. Although crocodiles and alligators have four chambered hearts, all members of reptile class have a semi- septa (the connective tissue dividing the four chambers of the heart in birds and mammals), and mixed blood running through their body.

Thly also are the first vertebrate class to have internal fertilization. This also is an adaptation for life on land. Their eggs are covered with a protective shell that prevents water loss and protects the embryo from environmental changes.

They are cold- blooded animals.

There are many different types of reptiles including snakes, lizards, turtles, tortoises, and crocodiles. Most are carnivores?, and may feed on many different preys including humans! Some species of turtles feed on plants.


If you were to define a bird, what would you say? The first common characteristic that ever comes to one’s mind is that they are “flying”! Of course, the birds are more than just “flying objects”. To be scientific, birds can be defines as reptile like animals that are warm- blooded. They have an outer covering of feathers; two legs that are covered with scales and are used for walking or perching; and the front extremities have changed as wings for flight.

birds lungsOne of the remarkable features of this group that distinguishes it from any other kind of animal group is their feathers. Feathers are made of protein, and provide clothing and insulation.

Their heart is four- chambered, and have a complete division that prevents the mixing of deoxygenated and oxygenated blood.

They respire by means of lungs, and their lungs have secondary extensions named air sacs which even reach inside the bones. Having air sacks is very important for birds because of two reasons: The first reason is that air sacs increase the total lung surface for the diffusion of gases; and the second reason is that flying is not as easy as it’s seen! In order to move in the air, first of all the bird has to lift its body against the gravitational force. If the mass of the bird is much, it will be very hard for it to lift itself. The air sacs occupy most of the volume of the lungs, and help the organism stay “light” enough for flight. If you have ever experienced holding a bird and a mouse in your hands, you will better understand. A bird is much lighter than a mouse which’s approximately of the same size.

They have no teeth but a beak or bill. They may be carnivores, herbivores, or omnivores.

Just like reptiles, birds also do internal fertilization and external development. When the birds mate, sperm from the male and egg from the female bird fuse. The large, shell covered eggs are incubated by parents, and after hatching, the parents take care of the youngs. Birds are the first group of animals that have maternal instincts.

Woodpeckers, pigeons, blackbirds, ducks, geese, eagles, hawks, vultures, ibis, ostriches, sea gulls, sparrows, and penguins are examples of birds.


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