Characteristics of Phylum Chordata


Introduction

Phylum Chordata is one of the most well-known and complex animal phyla, which includes all animals possessing a notochord, a dorsal hollow nerve cord, and pharyngeal gill slits at some stage of their life. This phylum encompasses animals ranging from simple organisms like tunicates to more complex vertebrates like mammals.

Characteristics of Phylum Chordata

  1. Notochord:
    • The notochord is a flexible, rod-like structure present in all chordates at some stage of development. It provides skeletal support and in many cases is replaced by the vertebral column in adult vertebrates.

 

Figure : Diagram of a typical chordate, highlighting the notochord, dorsal nerve cord, pharyngeal slits, and post-anal tail

Dorsal Hollow Nerve Cord:

    • The nerve cord in chordates is located dorsally (on the back) and is hollow. In vertebrates, this nerve cord develops into the brain and spinal cord (central nervous system).
  1. Pharyngeal Gill Slits:
    • Pharyngeal gill slits are openings in the pharynx (throat area) that are present in all chordates at some stage of development. In aquatic chordates like fish, they develop into gills, while in terrestrial animals, they may contribute to structures like the middle ear and tonsils.
  2. Post-anal Tail:
    • All chordates have a tail extending beyond the anus at some stage of development. In some chordates, this tail is retained in adulthood, while in others, it is only present during embryonic stages.

Image Reference: Diagrams illustrating chordate features, including the post-anal tail and pharyngeal slits, are available in NCERT Biology Class XI, Chapter 4.

  1. Closed Circulatory System:
    • Chordates have a well-developed closed circulatory system. Blood is circulated through vessels, and most chordates have a heart with chambers for efficient blood circulation.

Classification of Phylum Chordata

Phylum Chordata is divided into three major subphyla:

  1. Urochordata (Tunicata):
    • In this subphylum, the notochord is present only in the larval tail. Adults are usually sessile and marine.
    • Examples: Ascidia, Salpa, Doliolum.

Cephalochordata:

    • The notochord extends from the head to the tail and is retained throughout life. These animals are exclusively marine.
    • Examples: Branchiostoma (also known as Amphioxus).
  1. Vertebrata:
    • Vertebrates are characterized by the presence of a vertebral column (backbone) that replaces the notochord in adults. Vertebrates have a more complex brain, well-developed sensory organs, and paired appendages (fins or limbs).
    • Examples: Mammals, birds, reptiles, amphibians, fishes.

Economic and Ecological Importance of Chordates

  • Human Evolution and Development: Vertebrates include humans, making the study of this phylum crucial for understanding human anatomy and evolution.
  • Biodiversity: Chordates occupy various ecological niches, from aquatic environments (fishes) to terrestrial habitats (mammals, birds), contributing to biodiversity.
  • Food and Economy: Vertebrates such as fish, poultry, and livestock are essential sources of food for humans. Many species are also involved in agriculture, pet industries, and research.

Conclusion

Phylum Chordata is a diverse and complex group of animals that share common characteristics such as a notochord, dorsal hollow nerve cord, and pharyngeal gill slits. These features play a fundamental role in their development and adaptation to various environments.


Figure 2: Diagram of Branchiostoma (Amphioxus) showing the persistent notochord and pharyngeal gill slits.

Questions

Q 1. During its life cycle, Fasciola hepatica (liver fluke) infects its intermediate host and primary host at the following larval stages respectively;

(a) metacercaria and cercaria;

(b) miracidium and metacercaria;

(c) redia and miracidium;

(d) cercaria and redia;

Q 2. Bladderworm/cysticercus is the larval stage of;

(a) tapeworm;

(b) roundworm;

(c) pinworm;

(d) liver fluke;

Q 3. Which one of the following kinds of animals are triploblastic?;

(a) Flatworms;

(b) Sponges;

(c) Ctenophores;

(d) Corals;

Q 4. One example of animal having a single opening to the outside that serves both as mouth as well as anus is;

(a) Octopus;

(b) Asterias;

(c) Ascidia;

(d) Fasciola;

Q 5. Planaria possess high capacity of;

(d) bioluminescence;

(c) alternation of generation;

(b) regeneration;

(a) metamorphosis;

Q 6. Bilaterally symmetrical and acoelomate animals are exemplified by;

(d) Ctenophora;

(c) Annelida;

(b) Aschelminthes;

(a) Platyhelminthes;

Q 7. Biradial symmetry and lack of cnidoblasts are the characteristics of;

(d) Hydra and starfish;

(c) Aurelia and Paramecium;

(b) Ctenoplana and Beroe;

(a) Starfish and sea anemone;

Q 8. Organ pipe coral is;

(d) Fungia;

(c) Helipora;

(b) Astraea;

(a) Tubipora;

Q 9. Jelly fish belongs to class;

(d) None of these;

(c) Anthozoa;

(b) Scyphozoa;

(a) Hydrozoa;

Q 10. Budding is a normal mode of asexual reproduction in;

(d) sponge and starfish;

(c) tapeworm and Hydra;

(b) Hydra and sponges;

(a) starfish and Hydra;

Characteristics of Phylum Platyhelminthes


Introduction

Phylum Platyhelminthes, also known as flatworms, includes soft-bodied, bilaterally symmetrical animals with a flattened body. These organisms are the simplest animals to exhibit organ-level organization, and many are parasitic. Flatworms include free-living forms like Planaria and parasitic species such as Taenia (tapeworms).

Characteristics of Phylum Platyhelminthes

  1. Body Shape and Symmetry:
    • Platyhelminthes are bilaterally symmetrical, meaning their body can be divided into two equal halves along one plane.
    • Their body is dorsoventrally flattened, giving them a "flat" appearance, hence the name "flatworms."
  2. Organ System-Level of Organization:
    • Platyhelminthes exhibit an organ-system level of organization. While their organ systems are relatively simple, they do have specialized organs for excretion, reproduction, and digestion.
  3. Triploblastic:
    • These organisms are triploblastic, meaning their body is derived from three germ layers: ectoderm, mesoderm, and endoderm. This allows for greater tissue differentiation and the development of more complex organs compared to diploblastic organisms.
  4. Acoelomate:
    • Platyhelminthes are acoelomates, meaning they lack a true body cavity (coelom). The space between the body wall and digestive tract is filled with a mesodermal tissue called parenchyma.
  5. Digestive System:
    • The digestive system of flatworms is incomplete, with only one opening (the mouth). There is no separate anus, and digestion is both extracellular and intracellular.
    • In parasitic species, the digestive system may be reduced or absent, as they absorb nutrients directly from their host.