Tiêu đề Med-RM_Zoo_SP-2_Ch-11-Animal Kingdom (Chordates).pdf ✅

Chapter Contents Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Phylum Chordata I. Protochordata or Acraniata Sub-phylum : Urochordata Sub-phylum : Cephalochordata II. Craniata or Euchordata Sub-phylum : Vertebrata/ Craniata Superclass-1 : Pisces (i) Chondrichthyes (ii) Osteichthyes Superclass-2 : Tetrapoda (i) Amphibia (ii) Reptilia (iii) Aves (iv) Mammalia Animals that belong to chordates are fundamentally characterised by the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits. The notochord is replaced by a cartilaginous or bony vertebral column in adults in sub-phylum vertebrata, thus we say all vertebrates are chordates but all chordates are not vertebrates. Besides the basic chordate characters, vertebrates have a ventral muscular heart with two, three or four chambers, kidneys for excretion and osmoregulation and paired appendages which may be fins or limbs. PHYLUM CHORDATA Phylum chordata has four fundamental features. 1. Notochord (elastic, solid, ensheathed rod-like structure of vacuolated turgid cells which is present throughout the life or only during early embryonic development, located between nerve cord and digestive tube (alimentary canal). In vertebrates, notochord is replaced by a cartilaginous or bony vertebral column in adults. Nerve cord Pharynx Notochord Digestive tube Paired-gill slits Post-anal part Mouth Fig. : Chordata characteristics 2. Dorsal hollow nerve cord : It differentiates into brain and spinal cord. It is present above the notochord. Chapter 11 Animal Kingdom (Chordates)
166 Animal Kingdom (Chordates) NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 3. Paired pharyngeal gill slits : Take part in circulation of water for respiration. In higher chordates, they occur only in embryonic stage. 4. Post anal tail : It is present for balancing. Along with these features chordates are bilaterally symmetrical, triploblastic, coelomate with organ system level of organisation and close circulatory system. Table : Comparison of Non-chordates and Chordates Non-chordates Chordates Notochord present. Central nervous system is dorsal, hollow and single. Pharynx perforated by gill slits. Heart is ventral. A post-anal tail is present. Gut is ventral to nerve cord. Notochord absent. Central nervous system is ventral, solid and double. Gill slits are absent. Heart is dorsal (if present). Post-anal tail is absent. Gut is dorsal to nerve cord. 1. 2. 3. 4. 5. 6. 1. 2. 3. 4. 5. 6. Phylum chordata is divided on the basis of whether it has cranium (brain-box) or not. Phylum : Chordata Acraniata or Protochordata Urochordata/Tunicata Cephalochordata Vertebrata No brain box or cranium Cranium is present Craniata or Euchordata 2 sub-groups sub-phylum sub-phylum Notochord is present only in larval tail Notochord extends from head to tail region e.g. Ascidia Salpa Doliolum , , e.g. Branchiostoma I. PROTOCHORDATA OR ACRANIATA Sub-phylum - UROCHORDATA 1. The adult body is enclosed within a leathery test or tunic formed of a cellulose-like organic substance termed tunicin, therefore, this phylum is called tunicata. 2. Notochord is only present in the tail of the larva (hence named Urochordata) and disappears in the adult. 3. Circulatory system is open in tunicates. (b)(a) Branchial aperture Test or Tunic Atrial aperture Foot Fig.: (a) Ascidia, (b) Herdmania
NEET Animal Kingdom (Chordates) 167 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 4. Development is indirect. 5. Retrogressive metamorphosis shown by the larva i.e. change from better developed larva to less developed adult. 6. Excretion by neural gland. Examples : Ascidia, Salpa, Doliolum, Herdmania (sea squirt), Pyrosoma (colonial bioluminiscent form) Sub-phylum CEPHALOCHORDATA 1. Notochord extends from head to tail region. 2. Notochord persists throughout life. 3. Digestive tract is complete. Pharynx is perforated by numerous persistent gill-slits. 4. Circulatory system well-developed, closed and without heart. 5. Development indirect, including free swimming larva. 6. Respiration through general body surface. 7. Excretion by protonephridia with solenocytes. 8. Paired appendages absent. Median fins (dorsal, ventral and caudal) are present. Example : Branchiostoma (Amphioxus or Lancelet) Amphioxus has both ends pointed like lance, hence it is commonly called lancelet. Caudal fin Tail Dorsal fin Myocommata or Myosepta Dorsal fin-ray boxes Myotomes or Myomeres Rostrum Notochord Anus Ventral fin Ventral fin-rays boxes Atriopore Position of atrium Gonads Metapleural folds Oral hood Position of pharynx Buccal cirri Fig.: Amphioxus II. CRANIATA OR EUCHORDATA Sub-phylum VERTEBRATA/CRANIATA General characteristics of sub-phylum vertebrata : 1. Brain is enclosed within a cranium. 2. Possess notochord during the embryonic period only. 3. Notochord is replaced by a cartilaginous or bony vertebral column in the adult, thus all vertebrates are chordates but all chordates are not vertebrates. 4. Vertebrates have ventral muscular heart with two, three or four chambers. 5. Kidneys are present for excretion and osmoregulation. 6. For locomotion, they have paired appendages which may be fins or limbs. 7. They are unisexual. 8. They have single pair of gonads.
168 Animal Kingdom (Chordates) NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Sub-phylum - Craniata or Vertebrata Notochord is replaced by vertebral column Agnatha (lacks jaw) Ostracodermi e.g.Cephalaspis (Extinct) Placodermi (Extinct) e.g.Climatius Reptilia e.g.Chelone, Testudo Amphibia e.g.Bufo , Rana Pisces (bear fins) Gnathostomata (bears jaw) Cyclostomata e.g.Petromyzon , Myxine Osteichthyes e.g.Labeo , Hippocampus Mammalia e.g.Macropus , Pteropus Chondrichthyes e.g.Scoliodon , Pristis Aves e.g.Corvus , Columba Tetrapoda (bear limbs) Division Class Classes Classes 2 superclasses Division-1 : AGNATHA (The Jawless Vertebrates) 1. They are the most primitive of all craniates. 2. Mouth does not possess jaws, hence, named Agnatha. 3. Notochord persists throughout life. 4. They do not have exoskeleton and paired appendages. 5. They have a single nostril. 6. They are cold-blooded. CLASS 1. CYCLOSTOMATA General characteristics 1. All living members of this class are ectoparasites on some fishes. 2. They have an elongated body bearing usually 6-15 pairs of gill slits for respiration. 3. Cyclostomes have a sucking circular mouth. 4. Mouth is without jaws, hence, they are also called jawless fishes. 5. Their body is devoid of scales and paired fins. 6. Cranium and vertebral column are cartilaginous. 7. Circulation is of closed type. 8. Stomach is absent. 9. Cyclostomes are marine but some migrate for spawning to fresh water. After spawning, within a few days, they die. Their larvae, after metamorphosis, return to the ocean. Examples : Petromyzon (Lamprey) and Myxine (Hagfish).