The word Chordata is formed from the Latin word chorda meaning chord or notocord or string and ata meaning to bear. Organisms that have rodlike and elastic notochords and hollow nerve cords throughout life or at any stage of life are called chordata. Chordates make up about 3-5% of the world’s population. The number of non- Chordata is 68,500 (Hiclman, 2008). Scientist Balfour (1880) created the order Chordata with animals having notochords. Bateson first named the episode.
Characteristics of chordata
1. Vertebral Cord: Chordates have a notochord in embryo or throughout life. In advanced animals the notochord is replaced by the spinal cord.
2. Brain: Chordates have nerve cords. The anterior end of the nerve cord forms the brain.
3. Symmetry: The posterior part of the nerve cord of Chordata animals forms the symphysis.
4. Pharyngeal gill openings: Chordates have pharyngeal gill openings at any stage of life or throughout life.
5. Heart: Cordata animals have a well-formed heart. The heart is always located at the apex of the intestine.
6. Endostyle: Chordata animals have endostyle. The endostyle later transforms into the thyroid gland.
7. Digestive System: Chordata have complete digestive system. It contains intracellular and extracellular digestive glands.
8. Tail: Cordatas have a post-anal segment elastic tail. Sometimes the tail can get lost during the transition.
9. Circulatory system: Chordates have closed circulatory system. It is made up of blood, blood vessels and blood vessels. It has hepatic portal system.
10. Excretory system: The main excretory system of chordates consists of a pair of kidneys. Through this, nitrogenous wastes are removed from the body.
11. Body skin: The body skin of chordata animals consists of epidermis (derived from ectoderm) and dermis (derived from mesoderm).
12. Endoskeleton: The endoskeleton of chordates is made up of bone or cartilage.
13. Eyes: Cordatas eyes are simple in nature. It originates from the brain.
14. Legs: Vertebrate animals have two pairs of legs.
15. Segmentation: Segmentation of chordates is limited to body wall, brain and tail.
16. Genus: Chordata are unisexual. They have sex. Asexual reproduction is absent.
17. Osmoregulation: Osmoregulation of chordates occurs through the kidneys.
18. Silome: True silome is present in the body of chordates. Surrounding the heart is the pericardial cavity.
[key words to remember features: spinal cord, brain, mesentery, pharyngeal pharynx, endostyle, tail]