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Phylum Chordata, which is part of the Kingdom Animalia includes all vertebrates and invertebrates with or without a backbone. The chordates are a large, heterogeneous group of organisms that differ greatly in many ways.
- They have a body that is bilaterally symmetrical and are divided into three subphyla.
- Phylum Chordata is divided into Craniata or Vertebrata, Tunicata or Urochordata and Cephalochordata.
- The phylum is derived from the Greek word chord, which means string.
- The classification of phylum chordata have been proposed by a number of taxonomists from time to time due to the great diversity of chordate.
- These organisms have rigid, dorsal supporting rods at some point during their life cycle.
- Some examples of phylum Chordata include pandas, crows, sharks, owls and humans.
Key Terms: Phylum Chordata, Kingdom Animalia, Organisms, Characteristics of Phylum Chordata, Examples of Phylum Chordata, Vertebrates
What is Phylum Chordata?
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Phylum Chordata usually refers to the categories of animals with a rod-like structure, which is often referred to as the backbone or spine.
- It usually includes all types of animals that satisfy four basic characteristics, i.e., a notochord, pharyngeal slits, postanal tail and dorsal nerve cord.
- Phylum Chordata consists of five different types of animals, including amphibians, reptiles, mammals, birds and fish.
- These organisms have a tail that stretches behind and above the anus, along with a hollow nerve cord above the gut.
- The most well-known examples of these organisms include Lampreys and Sea Squirt.
Apart from the above mentioned characteristics, the Phylum Chordata is bilaterally symmetrical, triploblastic and segmented body whose design is complex and usually well differentiated.
Scientific Classification of Phylum Chordata
The scientific classification of phylum chordata are as follows:
- Kingdom - Animalia
- Subkingdom - Eumetazoa
- Clade - Parahoxozoa
- Clade - Bilateria
- Clade - Nephrozoa
- Superphylum - Deuterostomia
- Phylum - Chordata
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Characteristics of Phylum Chordata
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A brief description of each characteristic of phylum chordata has been presented to provide you with a clear understanding of the topic.
Post Anal Tail
This is considered to be an extension of the body to the anus, which comprises skeletal muscles that are known to help out in locomotion for species like fish. However, it can be absent from most adult chordates.
Notochord
The notochord is a longitudinal, cartilaginous rod-like structure running between the nerve cord and digestive tract. It acts as a support system for the nerve cord, which is replaced by the vertebral column following the embryonic stage in all vertebrates.
Pharyngeal Slits
They are the openings that allow water to enter the mouth without entering the digestive system, i.e. they connect the mouth and the throat. The chordates have such openings on the lateral sides of the pharynx at some point in their life.
Dorsal Nerve Cord
The Dorsal Nerve Cord is usually a bundle of nerves that run along the back and further split in the spinal cord and the brain. This cord is hollow and resides dorsal to the notochord.
Classification of Phylum Chordata
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Phylum Chordata can be further classified into three major categories of sub-phyla. These categories have been explained in a detailed manner for your convenience:
Urochordata
Urochordata, also known as tunicate, consists of the body of an adult chordate enclosed within a tunic-like structure made up of a cellulose-like substance called tunicin.
- The notochord in such chordates can be seen only during the larval stage, which further disappears in the adults.
- It is replaced by a dorsal ganglion.
- For Example: Ascidia, Salpa.
Cephalochordata
In such chordates, notochord is present throughout their lifetime and has well developed pharyngeal gill slits. They have their tails present in their entire lifetime and even show progressive metamorphosis. For Example: Lancelets
Vertebrata
Vertebrata are considered to be the advanced chordates that usually develop a cranium around the brain. Their notochord is replaced with a vertebral column in adults.
- Therefore, it is often speculated that vertebrates are chordates, but all chordates are not vertebrates.
- They are unisexual and reproduce sexually, along with having a well-developed respiratory system and excretory system.
- For example Humans.
Classification of Subphylum Vertebrata
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The subphylum Vertebrata can be further classified into following categories:-
Cyclostomata
Cyclostomata are ectoparasites located inside or on the skin of some fish. Their body comprises around 6-15 pairs of gill slits that help in respiration and have a circular mouth without jaws.
- These parasites are marine for spawning, after which they usually die within a few days of spawning.
- For example, Petromyzontia (Modern Lamprey) and Myxine (Hagfish).
Chondrichthyes
Chondrichthyes are marine animals that have a streamlined body, cartilaginous endoskeleton, two-chambered hearts and placoid scales on the body. These animals have their notochord present throughout their lifetime.
- Chondrichthyes are cold-blooded animals, i.e., they cannot decide the body temperature.
- For Example: Dogfish, Sawfish, Stingray, etc.
Osteichthyes
Animals belonging to this particular class are both saltwater and freshwater fishes with a bony endoskeleton and a streamlined body. They usually have a two-chambered heart, four pairs of gills, and a cycloid cover over the skin. Examples include flying Fish, Katla, Angelfish, etc.
Amphibia
This class of animals can live in both aquatic and terrestrial environments. They usually consist of two pairs of limbs, moist skin without scales, eyes with eyelids, etc.
- They have a three-chambered heart, gills and skin for respiration, along with lungs, mesonephric kidneys, central nervous system and ten pairs of cranial nerves.
- For example, toads, frogs, treefrogs, etc.
Reptilia
Most members reptilia are terrestrial, with dry cornified skin, epidermal scales, or scutes covering their bodies. They are considered to be oviparous, which means their development is direct. Examples include Turtles, Chameleons, Cobras, and Crocodiles.
Aves
The presence of feathers and the ability to fly are the most distinguishing characteristics of Aves, with the exception of some flightless birds, such as the ostrich. For Example: Pigeon, Crow, Penguin, etc.
Mammalia
This class's members are highly developed and advanced. Polar ice caps, deserts, mountains, forests, grasslands, and dark caves are just some of the places they can be found. For example, there are Platypus, Camel, Lion, Monkey, Elephant, Horse, etc.
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Examples of Phylum Chordata
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Various examples of phylum chordata are as follows:
- Fish
- Birds
- Marine squirts (tunicates)
- Lancelets (cephalochordates)
- Scoliodon
- Sphyrna
- Torpedo
Things to Remember
- Phylum Chordata usually refers to the categories of animals with a rod-like structure.
- It usually includes all types of animals that satisfy four basic characteristics, i.e., a notochord, pharyngeal slits, postanal tail and dorsal nerve cord.
- The largest group is vertebrates, which have more than 62,000 species.
- The characteristics of phylum Chordata include post-anal tail, notochord, pharyngeal slits and dorsal nerve cord.
- The seven specified classes of subphylum vertebrata are cyclostomata, chondrichthyes, osteichthyes, amphibia, reptilia and aves.
Sample Questions
Ques. Why all vertebrates are chordates but all chordates are not vertebrates? (2 marks)
Ans. Chordata has a subphylum called Vertebrata. A vertebral column, similar to the notochord, exists in Vertebrates. Vertebrates exhibit all of the Phylum Chordata's characteristics. However, the Phylum Chordata includes two subphyla: Urochordata and Cephalochordata. These are invertebrate animals, but they have some Chordate characteristics, such as the presence of a notochord. As a result, while all vertebrates are chordates, not all chordates are vertebrates.
Ques. What are the features of Phylum Chordata? (2 marks)
Ans. The features of Phylum Chordata include of the following:
- Post Anal Tail
- Notochord
- Pharyngeal Slits
- Dorsal Nerve Cord
Ques. What features of the Aves contribute to their flying capacity? (2 marks)
Ans. Some major features of Aves such as lightweight feathers that are smooth, pneumatic bones that are filled with air in the internal spaces, streamlined shape of body, etc. help them in maintaining their flying capacity.
Ques. What are the similarities between Aves and Mammals? (2 marks)
Ans. Homeotherms, or warm-blooded animals, include both Aves and Mammals. They have a heart with four chambers. Both the Aves and the mammals have backbones and they are called vertebrates and they are warm blooded animals. They possess the four chambered hearts. They also provide parental care to their young ones. The blood of these organisms has both red blood cells and the white blood cells in their body.
Ques. What are the seven classes of Subphylum Vertebrata? (2 marks)
Ans. The seven specified classes of Subphylum Vertebrata are as follows:
- Cyclostomata
- Chondrichthyes
- Osteichthyes
- Amphibia
- Reptilia
- Aves
- Mammalia
Ques. What is the difference between Chordates and Non Chordates? (3 marks)
Ans. The differentiation between Chordates and Non Chordates has been given below for your reference:
| Chordates | Non-Chordates |
|---|---|
| They usually have a Dorsal Notochord throughout their lifecycle or during the larval stage. | They do not have a Notochord |
| The chordates develop Pharyngeal Gill Slits at some stage of the life span. | Non-Chordates do not have any Pharyngeal Gill Slits. |
| They have a bilateral symmetry. | They can have radical, bilateral or even asymmetrical symmetry. |
| They have a Dorsal, Hollow, Single Nerve Cord. | They have a Ventral, Solid, Double Nerve Cord. |
Ques. Why are the echinoderms considered to be closer to the chordates compared to the phylum? (5 marks)
Ans. Echinoderms are similar to chordates in that they are deuterostomes, which means that the anal region develops before the mouth region. Their larvae are also protochordate-like. Echinoderms are deuterostome marine organisms.
- This phylum of animals bear a calcareous endoskeleton composed of ossicles covered by a spiny skin. Echinoderms possess a water-based circulatory system.
- The madreporite is the point of entry and exit for water for the water vascular system.
- The characteristic features of Chordata are a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
- Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets), together with the vertebrates.
- Most tunicates live on the ocean floor and are suspension feeders.
- Lancelets are suspension feeders that feed on phytoplankton and other microorganisms.
Ques. What are Cyclostomata? (3 marks)
Ans. Cyclostomata, sometimes called Cyclostomes, is a group of jawless fish. They are the only living representatives of the Agnatha infraphylum, an ancient lineage of vertebrates. Here's a breakdown of their key characteristics:
Distinctive Features:
- No Jaws: The defining characteristic of Cyclostomata is the complete absence of true jaws. This sets them apart from most other fish species.
- Round Mouth: Their mouths are circular or oval-shaped, often equipped with horny teeth or sucking discs for feeding. This is where the name "Cyclostomata" originates, meaning "round mouths."
- Cartilaginous Skeleton: Unlike bony fish, Cyclostomata has a cartilaginous skeleton, similar to sharks and rays.
Ques. What are Agnatha? (3 marks)
Ans. Agnatha is an infraphylum within the phylum Chordata, representing a group of jawless fish. They are the evolutionary ancestors of all jawed vertebrates, including fish with bony skeletons (like salmon or tuna) and all land animals with backbones (like humans!).
Key Characteristics of Agnatha:
- Jawless: The defining feature of Agnatha is the complete absence of jaws. This sets them apart from most other fish species and presents a challenge for feeding.
- Varied Skeletons: While some organisms had no hard skeleton, others possessed skeletons made of either cartilage (like sharks) or bone.
- Diversity of Body Forms: Agnatha existed in a variety of shapes and sizes, with some resembling modern eels and lampreys, while others were more armored and had unique head structures.
Ques. How is locomotion carried out in phylum chordata? (2 marks)
Ans. Chordates can move around by using their muscles. This is accomplished by the tail in tunicate larvae, the body undulations in cephalochordates, and the general body motions (like those of eels and snakes) and limbs and fins (which in birds and certain mammals develop into wings) in vertebrates.
Ques. Where is notochord located? (3 marks)
Ans. In chordates, the notochord is located along the rostral-caudal axis of the body, which refers to the head-to-tail axis of the body.
- Dorsal to the gut tube: The notochord sits above the digestive system, also known as the gut tube.
- Ventral to the dorsal nerve cord: It's positioned below the main bundle of nerves running along the back, called the dorsal nerve cord.
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