Chordates
A chordate is an animal that belongs to the phylum Chordata, which becomes part of the Deuterostomes kingdom.
- Organisms in the Deuterostomes kingdom have a unique characteristic: their anus develops before their mouth in early embryonic phases.
- The phylum Chordata consists of a wide variety of organisms, as it consists of all vertebrates, which are organisms with a backbone, and many invertebrates; organisms that don’t have a backbone.
- There are 3 subphyla to Chordata: Cepahlochordata, Urochordata, and Vertebrata.
- Chordates usually have bilaterally symmetric bodies, though a couple of exceptions exist, and they share distinct characteristics.
Characteristics of Chordata
Chordates have all of these attributes, at least at some point in their lives. In many cases, these characteristics only appear during embryonic development. (embryogenesis).
Notochord
The chordates are called for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species. It is located between the digestive tube and the nerve cord, offering skeletal support through the length of the body. In some chordates, the notochord acts as the primary axial support of the body throughout the animal’s lifetime.
In vertebrates, the notochord exists during embryonic development, at which time it induces the development of the neural tube which acts as a support for the developing embryonic body. The notochord, however, is changed by the vertebral column (spinal column) in most adult vertebrates.
Dorsal Hollow Nerve Cord
The dorsal hollow nerve cord originates from an ectoderm that rolls into a hollow tube throughout development. In chordates, it lies dorsally (at the top of the animal) to the notochord. In contrast to the chordates, other animal phyla are defined by solid nerve cords that are located either ventrally or laterally. The nerve cord found in most chordate embryos turns into the brain and spinal cord, which consist of the central nervous system.
Pharyngeal Slits
Pharyngeal slits are openings in the pharynx (the area simply posterior to the mouth) that extend to the external environment. In organisms that live in water environments, pharyngeal slits permit the exit of water that enters the mouth during feeding. Some invertebrate chordates use the pharyngeal slits to filter food out of the water that enters the mouth. In vertebrate fishes, the pharyngeal slits develop into gill arches, the bony or cartilaginous gill supports.
In many terrestrial animals, including mammals and birds, pharyngeal slits are present only throughout embryonic development. In these animals, the pharyngeal slits become the jaw and inner ear bones.
Post-anal Tail
The post-anal tail is a posterior elongation of the body, extending beyond the anus. The tail contains skeletal elements and muscles, which offer a source of locomotion in aquatic species. In some terrestrial vertebrates, the tail also assists with balance, courting, and signaling when a threat is nearby. In humans and other apes, the post-anal tail exists throughout embryonic development, however is vestigial as an adult.
Other Characters of Chordates
These include bilateral symmetry, three germinal layers, segmentation, organ-system level of organization, cephalization, coelom, endoskeleton, complete digestive tract, special organs for respiration and excretion, closed circulatory system, different sexes, gonads with gonoducts, and without asexual reproduction.
Classification of Phylum Chordata
Phylum Chordata is classified into 3 subphyla, particularly.
- Urochordata (tunicates)
- Cephalochordata (lancelets)
- Vertebrata (vertebrates)
The subphylum Urochordata and Cephalochordata are jointly known as protochordates, which are marine animals. They are invertebrates but they share attributes of chordates.
Urochordata
- The adults are fixed to the substratum.
- It is likewise known as Tunicate due to the fact that the body of an adult is enclosed within a tunic made up of a cellulose -like compound called tunicin.
- Notochord can be seen just in the larval phase and disappears in the grownups.
- The nerve chord present in the larva is replaced by a dorsal ganglion in adults.
- The larva can move and undergoes a metamorphosis.
- For e.g., Ascidia, Salpa, Doliolum.
Cephalochordata
- The atrium exists.
- Motile adult and larval phase.
- The tail exists throughout life.
- They show the progressive transformation.
- The notochord is found throughout life.
- Numerous strong pharyngeal gill slits are present.
- For e.g., Lancelets have the notochord and nerve cable throughout their life. Nevertheless, they lack the brain and bony vertebral column like Branchiostoma.
Vertebrata
The characteristic features of vertebrates consist of:
- These are advanced chordates and have a cranium around the brain.
- The notochord is replaced by a vertebral column in adults. This is why it is stated that ‘all vertebrates are chordates however all chordates are not vertebrates’.
- A high degree of cephalization is present.
- The epidermis has many layers.
- They include three kinds of muscles-striped, unstriped and cardiac.
- They have a well-developed coelom.
- The alimentary canal is complete.
- The heart is three or four-chambered.
- They have proper and fully developed breathing and excretory systems.
- Endocrine glands are present in all.
- They are unisexual and reproduce sexually, hagfish being an exception.
For e.g., humans
Subphylum Vertebrata is further classified into 7 classes. They are:
MCQs with Answers
- What is a chordate?
- a) An invertebrate animal
- b) An animal belonging to the phylum Chordata
- c) An organism without a backbone
- d) A marine species
Answer: b
- How many subphyla are there in Chordata?
- a) Two
- b) Three
- c) Four
- d) Five
Answer: b
- What is the unique characteristic of organisms in the Deuterostomes kingdom?
- a) Mouth develops before the anus
- b) Anus develops before the mouth
- c) Both develop simultaneously
- d) Lack of mouth and anus
Answer: b
- Which structure provides skeletal support through the length of the body in some chordates?
- a) Brain
- b) Nerve cord
- c) Notochord
- d) Tail
Answer: c
- Where does the dorsal hollow nerve cord originate from?
- a) Endoderm
- b) Mesoderm
- c) Ectoderm
- d) Notochord
Answer: c
- What do pharyngeal slits develop into in vertebrate fishes?
- a) Gills
- b) Eyes
- c) Jaws
- d) Limbs
Answer: a
- What is the function of the post-anal tail in aquatic species?
- a) Locomotion
- b) Digestion
- c) Sensory perception
- d) Reproduction
Answer: a
- Which of the following is a subphylum of Phylum Chordata?
- a) Annelida
- b) Cephalopoda
- c) Urochordata
- d) Arthropoda
Answer: c
- Which subphylum includes marine animals known as protochordates?
- a) Urochordata
- b) Cephalochordata
- c) Vertebrata
- d) Both a and b
Answer: d
- In which subphylum does the notochord persist throughout life?
- a) Urochordata
- b) Cephalochordata
- c) Vertebrata
- d) Both a and b
Answer: b
- What is a distinguishing feature of Subphylum Vertebrata?
- a) Presence of notochord
- b) Cranium around the brain
- c) Motile larval phase
- d) Marine habitat
Answer: b
- Which class in Subphylum Vertebrata includes humans?
- a) Mammalia
- b) Aves
- c) Reptilia
- d) Osteichthyes
Answer: a
- What replaces the notochord in adult vertebrates?
- a) Brain
- b) Spinal cord
- c) Vertebral column
- d) Tail
Answer: c
- How many layers does the epidermis have in vertebrates?
- a) One
- b) Two
- c) Three
- d) Many
Answer: d
- Which of the following is not a characteristic of vertebrates?
- a) Striped muscles
- b) Well-developed coelom
- c) Incomplete digestive tract
- d) Complete respiratory system
Answer: c
FAQs
1. What defines an animal as a chordate?
- A chordate is an animal belonging to the phylum Chordata, characterized by the presence of a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some point in their life.
2. How is the phylum Chordata classified?
- The phylum Chordata is classified into three subphyla: Urochordata, Cephalochordata, and Vertebrata.
3. What is the unique characteristic of the Deuterostomes kingdom?
- In the Deuterostomes kingdom, the anus develops before the mouth in early embryonic phases.
4. What is the function of the notochord in chordates?
- The notochord, a flexible rod-shaped structure, provides skeletal support through the length of the body during embryonic development and in some species throughout their lifetime.
5. How does the dorsal hollow nerve cord originate?
- The dorsal hollow nerve cord originates from the ectoderm, rolling into a hollow tube during development. It lies dorsally to the notochord in chordates.
6. What do pharyngeal slits develop into in vertebrate fishes?
- In vertebrate fishes, pharyngeal slits develop into gill arches, which are bony or cartilaginous structures that support the gills.
7. Does the post-anal tail persist in humans?
- The post-anal tail exists in humans and other apes during embryonic development but is vestigial as an adult.
8. What are some other characteristics of chordates?
- Chordates exhibit bilateral symmetry, three germinal layers, segmentation, organ-system level of organization, cephalization, coelom, endoskeleton, complete digestive tract, special organs for respiration and excretion, closed circulatory system, and more.
9. How is Subphylum Vertebrata different from the other subphyla?
- Subphylum Vertebrata is characterized by having a cranium around the brain, the notochord being replaced by a vertebral column in adults, a high degree of cephalization, and several advanced features in comparison to Urochordata and Cephalochordata.
10. Which classes are included in Subphylum Vertebrata?
Subphylum Vertebrata includes Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia.
11. Are all chordates vertebrates?
No, while all vertebrates are chordates, not all chordates are vertebrates. Chordates also include invertebrates like Urochordata and Cephalochordata.
Summary:
The tutorial on Chordates provides a comprehensive overview of the characteristics, developmental stages, and classification within the phylum Chordata. Key points covered include:
- Chordates Definition and Classification:
- Chordates are animals belonging to the phylum Chordata, characterized by a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. The phylum is divided into three subphyla: Cepahlochordata, Urochordata, and Vertebrata.
- Characteristics of Chordates:
- Chordates exhibit bilateral symmetry, three germinal layers, segmentation, organ-system level of organization, cephalization, coelom, endoskeleton, complete digestive tract, and more. These traits are evident at some point in their lives, often during embryonic development.
- Notochord:
- The notochord, a rod-shaped structure, provides skeletal support during the embryonic stage and, in some species, throughout their lifetime. In vertebrates, it induces the development of the neural tube, later replaced by the vertebral column.
- Dorsal Hollow Nerve Cord:
- The dorsal hollow nerve cord originates dorsally to the notochord, developing into the brain and spinal cord. This distinguishes chordates from other animal phyla with solid nerve cords.
- Pharyngeal Slits:
- Pharyngeal slits, openings in the pharynx, aid in water exit during feeding in aquatic environments. In vertebrates, these slits develop into gill arches, supporting the gills.
- Post-anal Tail:
- The post-anal tail, a posterior elongation, assists in locomotion in aquatic species and serves various functions in terrestrial vertebrates. In humans, it exists during embryonic development but is vestigial as adults.
- Other Characters of Chordates:
- Additional characteristics include various anatomical features, closed circulatory systems, different sexes, and reproductive methods.
- Classification of Phylum Chordata:
- Phylum Chordata is classified into Urochordata (tunicates), Cephalochordata (lancelets), and Vertebrata (vertebrates). Vertebrates, the advanced chordates, have distinct features like a cranium, vertebral column, and well-developed organ systems.
- Subphylum Vertebrata Classes:
- Subphylum Vertebrata is further divided into seven classes, encompassing various vertebrate animals.
This tutorial provides a comprehensive understanding of chordates, covering their defining features, evolutionary aspects, and the diversity within the phylum.