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Vertebrata

Introduction:

  • Under craniata there is only one phylum therefore terms Craniata and Vertebrata can be used replacably
  • The animals belonging to subphylum Vertebrata possess notochord during the embryonic stage while in adults, the notochord is replaced by a cartilaginous or bony vertebral column.
  • Thus, all vertebrates are chordates but all chordates are not vertebrates.

Topics covered

  • Agnatha
  • Gnathostomata

Detailed explanation:

  • Vertebrates possess ventral muscular heart with two, three or four chambers,
  • Kidneys are found in them for excretion and osmoregulation.
  • They usually have paired appendages (fins or limbs).
  • They possess a closed circulatory system which consists of the blood vascular and lymphatic system.
  • Hepatic portal system is present.
  • Respiration may occur through respiratory organs like gills, skin, buccopharyngeal cavity and lungs.
  • They possess a very high degree of cephalization (formation of head).
  • They have cranium (brain box) around the brain.
  • Nervous system consists of -
    - Central nervous system (brain and spinal cord)
    - Peripheral nervous system (cranial and spinal nerves).
    - 8, 10 or 12 pairs of cranial nerves.
    - Autonomic nervous system (sympathetic and parasympathetic)
  • They are unisexual.
  • Asexual reproduction is absent.
  • Sense organs are present like ear, eyes, tongue, nasal chambers and skin.

Classification of subphylum Vertebrata -

Subphylum Vertebrata is divided into two divisions -

a. Agnatha
b. Gnathostomata

Agnatha
 

Introduction:

  • These are the jawless vertebrates. Thus, they are called Agnatha.
  • They possess notochord throughout their life.
  • Vertebral column is present in the form of small imperfect neural arches over the notochord.
  • 8 or 10 pairs of cranial nerves are present.
  • Paired appendages are absent.
  • They possess a single nostril.
  • They are cold blooded animals.

Detailed explanation
 

Group Agnatha is divided into two classes -
a. Class Ostracodermi
b. Class Cyclostomata

Ostracodermi
 

  • These were the first vertebrates.
  • Found in freshwater.
  • All the members belonging to this class are extinct.
  • Their body is covered with a protective covering made up of hard scales.
  • Example - Cephalaspis

Cyclostomata
 

  • Class of round mouthed, fish-like, jawless vertebrates.

Habit and habitat

  • These are found in seawater (marine)
  • False fishes
  • Ectoparasites on true fishes.

Body

  • Streamlined body
  • Scale less, smooth body surface

Digestive system-

  • Complete digestive system
  • They have a sucking and circular mouth that lacks jaws. Hence, they are not true fishes or jawless vertebrates.
  • Sanguivores
  • Stomach and pancreas absent.

Respiratory system-

  • They have 6-15 pairs of gill slits which help in respiration.

Circulatory system

  • Circulatory system is closed.
  • Their heart is two chambered (1 auricle and 1 ventricle).

Excretory system-

  • Mesonephric kidney is present.
  • Uricotelic.

Locomotion-

  • Unpaired fins are present.

Skeleton-

  • Their cranium and vertebral column are cartilaginous.
  • Bones are absent.

Nervous system-

  • 10 pairs of cranial nerves.
  • They have a poorly developed head and brain.
  • Both notochord and vertebral columns are present.

Sensory organs-

  • Only 1 nostril is present i.e monorhynous.
  • Their internal ear which works as a statoreceptor (balancing) contains one or two semicircular canals.
  • One pair of lateral and 1 unpaired medial eye present.

Reproduction-

  • They are unnisexual
  • Fertilisation is external.

Development-

  • Development is direct except for Petromyzon.
  • They migrate towards freshwater for spawning and they die within a few days after spawning.
  • Their larvae return back to the ocean after metamorphosis.

Examples
 

1. Petromyzon

  • They are commonly known as lamprey.
  • They show anadromous migration.
  • Development is indirect in them i.e. Ammocoete larvae are formed.
  • Ammocoete larva is considered as the connecting link between Cephalochordata and Cyclostomata.

    petromyzon
     

2. Myxine

  • They are commonly known as hagfish.

Gnathostomata
 

Introduction:

  • Jawed vertebrates.
  • They possess notochord in the embryonic stage while in adults it gets replaced by a vertebral column.

Detailed explanation:

  • 10 or 12 pairs of cranial nerves are present.
  • Paired appendages like fins or limbs may be present.
  • They possess paired nostrils.
  • They have Cartilaginous or bony skeleton.
  • Mesonephric or metanephric kidneys present.
  • Unisexual animals
  • Sexual reproduction present

Classification of Gnathostomata -

Group Gnathostomata is divided into two super classes -
a. Superclass - Pisces
b. Superclass - Tetrapoda

Frequently Asked Questions: FAQs

Q1. Why are all vertebrates chordates but all chordates are not vertebrates ?
Ans :

  • The animals belonging to subphylum Vertebrata possess notochord during the embryonic stage while in adults, the notochord is replaced by a cartilaginous or bony vertebral column.
  • Thus, all vertebrates are chordates but all chordates are not vertebrates.

Q2. How many pairs of gill slits are present in the members of class belonging to class Cyclostomata ?
Ans :

  • The members belonging to class Cyclostomata have 6-15 pairs of gill slits which help in respiration.

Q3. Define monorhynus.
Ans :

  • Monorhynus condition is the presence of one/unpaired nostril.

Q4. What is the common name of Petromyzon ?
Ans :

  • Lamprey

Q5. Define anadromous migration.
Ans :

  • Anadromous migration is the migration of marine fishes into freshwater bodies for spawning.

Q6. What is the name of the larvae of Petromyzon ?
Ans :

  • Ammocoete larvae

Q7. What is the common name of Myxine ?
Ans :

  • Hagfish

Q8. Which larva is the connecting link between Cephalochordata and Cyclostomata ?
Ans :

  • Ammocoete larvae

Q9. What are the characteristics of Gnathostomata ?
Ans :

  • They are the jawed vertebrates.
  • They possess notochord in the embryonic stage while in adults it gets replaced by a vertebral column.
  • 10 or 12 pairs of cranial nerves are present.
  • Paired appendages like fins or limbs may be present.
  • They possess paired nostrils.
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