PHYLUM CHORDATA
Phylum Chordata: -In the scheme of classification, the Animal Kingdom is divided first into several major animal groups called phyla (singular, phylum). There are approximately 30 animal phyla currently recognized. The last major group of the Animal Kingdom is known as phylum Chordata. It was created by Balfour in 1880. The name of this phylum is derived from two Greek words, the chorde meaning a string or cord, and Ata meaning bearing. The reference is to a common characteristic feature in the form of a stiff, supporting rod-like structure along the back, the otochord (Gr., noton, back; L., chorda, cord), which is found in all the members of the phylum at some stage of their lives. Thus, chordates are animals having a cord, i.e., notochord. The animals belonging to all other phyla of the Animal Kingdom are often termed 'the non-chordates' or 'the invertebrates* since they have no notochord or backbone in their body structure. About 50,000 species present in this phylum.
Diversity of chordates: -
The chordates exhibit an astonishing diversity of form, physiology and habit. Numerical strength. The attribute of chordate species is not unusually large About 49,000 species are on record which are only half of the living species of molluscs, and less than one-tenth hose of arthropods. The two subphyla Urochordata and Cephalochordates claim for nearly 2,500 species. The subphylum Vertebrata includes 46,500 species; of these, fishes are the most numerous with approximately 25,000 species. It is commonly assumed that amphibian species number about 2,500, reptiles 6,000, birds 9,000 and mammals 4,500.
Three Fundamental Characters of Chordate: -
All the chordates possess three outstanding unique characteristics at some stage in their life history. These three fundamental morphological features include:
(1) A dorsal hollow or tubular nerve cord
(2) A longitudinal supporting rod-like notochord
(3) A series of pharyngeal gill slits
These three distinctive features, which set chordates apart from all other phyla, are so important that each merits a short description of its own.
Comparison (Differences) of Chordata with Non-Chordata: -
Features Chordata Nonchordata
1. Symmetry Bilateral Radial, biradial, bilateral or lacking
2. Metamerism True metamerism True or pseud or lacking
3. Post-anal tail Usually present Lacking
5. Germ layers 3, triploblastic 2 (diploblastic), 3 (triploblastic) or lacking
6. Coelom Truly coelomate Acoelornate, pseudocoelomate or truly coelomate
7. Limb derivation From several segments From same segment
8. Notochord Present at some stage or Notochord or backbone replaced by a backbone lacking made of ring like vertebrae
9. Gut position Ventral to nerve cord Dorsal to nerve cord
10. Pharyngeal gill-slits Present at some stage of life Absent 11. Anus Differentiated and opens Opens on the last before the last segment segment or absent
12. Blood vascular system Closed Open, closed or absent
13. Heart Ventrally placed Dorsal, lateral or absent
14. Dorsal blood vessel Blood flows posteriorly Blood flows anteriorly
15. Hepatic portal system Present Absent
16. Haemoglobin In red blood corpuscles In plasma or absent
18. Nervous system Hollow Solid
General Characters of Phylum Chordata: -
- Aquatic, aerial or terrestrial. All free-living with no fully parasitic forms.
- Body small to large, bilaterally symmetrical and metamerically segmented.
- A postanal tail usually projects beyond the anus at some stage and may or may not persist in the adult.
- Exoskeleton often present; well developed in most vertebrates.
- Body wall triploblastic with 3 germinal layers: ectoderm, mesoderm and endoderm.
- Coelomate animals having a true coelom. enterocoelic or schizocoel in origin.
- A skeletal rod, the notochord, present at some stage in life cycle.
- A cartilaginous or bony, living and jointed endoskeleton present in the majority of members (vertebrates).
- Pharyngeal gill slits present at some stage; may or may not be functional.
- Digestive system completes with digestive glands,
- Blood vascular system closed. Heart ventral with dorsal and ventral blood vessels. Hepatic portal system well developed.
- Excretory system comprising proto-or meso-or meta-nephric kidneys.
- Nerve cord dorsal and tubular. Anterior end usually enlarged to form brain.
- Sexes separate with rare exceptions.
IMPORTANT QUESTIONS: -
» Long Answer Type Questions: -
1. Discuss the features in which Chordates show an advancement over Non chordates.
2. Discuss the similarities and differences between Chordates and higher chordates in detail.
3. Classify Phylum Chordata up to classes giving the important characters and examples of each group.
Short Answer Type Questions: -
1. Give the main characteristics of phylum Chordata.
2. Draw a comparison between chordates and non-chordates.
3. Distinguish between— (i) Protochordate and Euchordata,(ii) Acrania and Craniata, (iii) Agnatha and Gnathostomata, iv) Pisces and Tetrapoda.
4. Write short notes on— (i) Chorda dorsalis, (ii) Pharyngealgill slits, (iii) Hernichordata, (iv) Urochordata, (v) Tetrapoda.
MULTIPLE CHOICE QUESTION: -
1. Which of this is not a chordate character?
(a) A dorsal or hollow tubular nerve cord (b) A longitudinal supporting rod-like notochord
(c) A series of pharyngeal gill slits (d) Diploblastic
2. Notochord is confined to proboscis in: -
(a) Urochordata (b) Hernichordata
(c) Cephalochordata (d) Chordata
3. Placoid scales are present in: -
(a) Hippocampus (b) ScoUodon
(c) Labeo (d) Protopterus
4. First jawed vertebrates belong to class: -
(a) Cyclostomata, (b) Placodermi
(c) Ostracodermi ' (d) Chondrictheys
5. The endoskeleton of chordate animals is: -
(a) Living structure (b) Living structure without growth
(c) Living structure with growth (d) Non-living structure
6. Which of the following is present in all chordates?
(a) Umbilical cord (b) Ventral tubular nerve cord
(c) Dorsal tubular nerve cord (d) Pseudocoelom
7. One of the following primitive class of chordates containing Amphiaxus and a few related forms, which are all marine: -
(a) Cephalochordata (b) Urochordata
(c) Hernichordata (d) Vertebrata
8. Which of the following is a chordate but not a vertebrate?
(a) Catta (b) Hippocampus
(c) Hemidactyius (d) Amphioxus
9. Name the primitive worm like animals having certain chordate features such as gill clefts and a small notochord in the anterior region of the head only: -
(a) Cephalochordate (b) Hernichordata
(c) Urochordata (d) None of the above
10. Which of the following is not a characteristic of members of Urochordata or Tunicata :
(a) Notochord and hollow central nervous system are present only in the larval stage
(b) The body is externally covered by a thick cellulose cuticle or tunic
(c) The coelom is absent (d) None of the above
11. Name the animal group whose members are considered doubtful chordates
(a) Urochordata (b) Hernichordata
(c) Cephalochordata (d) All of the above
12. Which of the following is a characteristic of members of the subphylum Urochordata?
(a) Worm-like animals that live in burrows, in the muddy bottom of the shore
(b) Cranium or brain box distinct (c) Both the notochord and the nerve cord are well developed
(d) Notochord found in larva and is confined to the tail only
13. Chordates with a backbone are called: -
(a) Invertebrates (b) Protochordates
(c) Vertebrates (d) Hemichordates
14. Which of the following animals is not a vertebrate?
(a) Fish (b) Frog (c) Sea horse (d) Sea squirt
15. Scales in the sharks are: -
(a) Cycloid (b) Ctenoid (c) Placoid (d) Ganoid
16. Which of the following is anamniote animal?
(a) Labeo (b) Crucodilus (c) Columba (d) Rattus
ANSWER KEY :-
1. (d) 2. (b) 3. (b) 4. (b) 5. (c) 6. (c) 7, (a) 8. (d) 9. (b) 10. (d) 11. (b) 12. (d) 13, (c) 14. (d) 15. (c)
16. (a)
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