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.
  
  
   

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.