Animal Taxonomy Part 1: Phylum Chordata Characteristics
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Animal Taxonomy Part 1: Phylum Chordata Characteristics

Learn about the key characteristics of animals in the phylum Chordata, including the presence of a notochord and a dorsal nerve cord. Explore the unique features that define chordates at different life stages.

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Study Notes

Phylum Chordata

  • Phylum Chordata is the most notable phylum, including all human beings, animals, and birds.
  • The distinguishing character of all animals in this phylum is the presence of notochord.
  • Chordates show four features at different stages in their life:
  • Notochord
  • Dorsal Nerve Cord
  • Post-anal tail
  • Pharyngeal slits

Dorsal Nerve Cord

  • A bundle of nerve fibers that connects the brain, muscles, and other organs.
  • Formation of Nerve Cord: a dorsal, hollow, longitudinal rod made of cartilage, running between the nerve cord and the digestive tract.
  • Its main function is to support the nerve cord.

Pharyngeal Slits

  • Openings that connect the mouth and the throat.
  • Allow the entry of water through the mouth, without entering the digestive system.

Subphylum Craniata

  • Occupy almost every environment: surface of the earth, marine and freshwater habitats, and terrestrial habitats.
  • Primitive members are agnathans (without jaws), lacking rigid hinged elements supporting the borders of the mouth.
  • Most members have the vertebral column that replaces the notochord and are called vertebrates.
  • They possess jaws and are known as Gnathostomata.

Common Features of Craniate

  • Bilateral symmetry: the arrangement of the organ systems in the right and left halves of the animal is exactly similar.
  • Cephalization: the anterior end of the animal is differentiated into a distinct head region.

Body Organization

  • Body is divisible into three regions: head, trunk, and tail.
  • Possess a well-developed head region and cranium.
  • Notochord is replaced by vertebral column either partly or wholly in the adult.
  • Nerve cord is differentiated into brain and spinal cord in the adult.

Organ Systems

  • Possess well-developed organ systems showing a higher grade of organization and functional efficiency.
  • Circulatory system: blood is confined to arteries, veins, and sinusoids with a well-developed muscular heart with two, three, or four chambers.
  • Respiratory system: in the lower forms, by paired gills, and in terrestrial species, by lungs.
  • Excretory system: the paired excretory organs (kidneys) discharge through ducts or ureters near or through the anus.
  • Nervous system: the brain becomes regionally differentiated as to structure and function.

Reproductive System

  • The sexes are separate, and each has a pair of gonads.
  • Development of the embryos may take place in different ways, and they can be: Oviparous, Ovoviviparous, and Viviparous.

Endocrine Glands

  • Provide hormones, transported by the bloodstream, that regulate bodily processes, growth, and reproduction.

Division (i): Agnatha

  • Marine or freshwater forms, distinct from other Vertebrates in the absence of jaws and paired fins or appendages.

Division (ii): Gnathostomata

  • Higher vertebrates possessing true jaws.
  • In most vertebrates, the embryonic notochord is replaced by a vertebral column.
  • They are further divided into two superclasses: Pisces and Tetrapoda.

Superclass: Pisces

  • Includes cartilaginous and bony fishes.
  • Mouth terminal or subterminal with different types of feeding habitats.
  • Four pairs of gills present, covered by a flexible plate called an operculum.
  • Gills are filamentary type, and an air bladder or swim bladder is often present.

Superclass: Tetrapoda

  • Means "four legs".
  • All tetrapods have a basic pentadactyl (five-digit) limb structure.
  • Amphibians, reptiles, birds, and mammals are the major groups of the Tetrapoda.
  • Tetrapods include all land-living vertebrates and also include a number of animals that live in the water, such as sea turtles, sea snakes, whales, and dolphins.

Class: Amphibia

  • Amphibians are the first tetrapods showing many transitional modifications from aquatic to terrestrial life.
  • The name Amphibia refers to a double life, leading a life both on land and in water.
  • They are partially terrestrial, as they have to return to water for breeding and development.
  • Cold-blooded vertebrates, viviparous vertebrates which give birth to young ones, except monotremes which are egg-laying mammals.

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