Subphylum - Vertebrata | Biology for JAMB PDF Download

Introduction

• One of the ways life is classified is through the presence or absence of the vertebrate. 
• Vertebrates and invertebrates evolved from a common ancestor that was speculated to have lived around 600 million years ago.
• Evidence of true vertebrates began to appear 525 million years ago and ever since then, vertebrates have branched off into a long lineage that includes armoured fish and giant sauropods to woolly mammoths and modern man.

Subphylum: Vertebrata

Characteristics of Vertebrata

– In these animals, notochord is completely or partially replaced by vertebral column.

  Vertebral column is made up of many vertebrae.

– Brain is covered by a protective covering made up of bones or cartilage, calledcranium.

– There is a prominant head and well developed and complicated brain.

–    Nerve cord remain enclosed within the vertebral column.

– Single or paired nostrils.

–   2 - 3 semicircular canals in each internal ear. 

– Animals are unisexual.

Classification of Vertebrata

Sub-phylum Vertebrata is further divided into two division.

1) Agnatha   (2) Gnathostomata

1. Agnatha (Jawless) :

– Jaws are absent in these animals .

– Notochord persistant.

– Mouth at the anterior end of body, round, funnel shaped and suctorial.

– Paired appendages (fins) are absent.

–    Single nostril. (Monorhynous)

–    cold blooded.

– Genital ducts are absent.

– Two semi - circular canals are found in internal ear.

– One median pineal eye is found along with lateral eyes on head. 

Group Agnatha is divided into two classes. (Only one is living)       

Class-Cyclostomata :

– Mostly marine, except some fresh water species.

– These are parasite as well as scavanger.

– Also called as Jawless fishes (false - fishes).

 – Body long, thin, tubular, tail  is flat.

– Skin soft,  smooth and scaleless. 

– Mouth is rounded, sucker like and biting - eating type.

– Three eyes are found on the head, one medain pineal eye and two lateral eyes.

– Only one Nostril (Monorhynous).

– Internal ear contains one or two semicircular canals. Internal ear works as statoreceptor only. ie. Organ of balance.  

– Gill clefts are 6 to 15 pairs.

– Digestive system is without stomach. Intestine has spiral typhlosole.

– Notochord and vertebral column both are present. Cranium and Vertebral column is made up of cartilage.

–   Bones are absent.

– Heart is two - chambered. It is called Venous - heart.

– Kidneys are protonephric or mesonephric type. 

– Paired fins absent. Dorsal median and tail fin is present.

– Tail is protocercal type. In this type of tail, notochord is extended at the last end of tail and tail fin is divided into two equal dorsal and ventral lobes.

– Animals unisexual, fertilization external, larval stage absent,

–   In Petromyzon - Ammocoete larva is present.

Petromyzon or Lamprey :

–    It is a living fossil.

–    Shows Anadromous migration. 

Larva Ammocoete is considered as connecting link between Cephalochordata and Cyclostomata.

–    It has wrinkled lips just like an old woman.

–    It usually remain attached with the gills of host.

–    It has Archaenephric kidney in young ones i.e. which can filter blood and coelomic fluid.

2. Gnathostomata

– Mouth is surrounded by true jaws.

– Vertebral column well developed.

– Movement by paired fins or legs.

– Gonads are paired, genital ducts are present.

– 3 Semi circular canals are found in internal ear.

– Pineal eye is absent.

– Animals are unisexual.

– Gills or lungs are meant for respiration.

 – Gnathostomata is classified into two super classes on the basis of locomotory organs, respiratory organs, heart and blood vascular system.

Super Class : - [1]  Pisces  [2] Reptilia  [3] Amhibia  [4] Aves  [5] Mammalia

Myxine or Hag fish : -

Ectoparasite (Sanguivorous) on true fishes. Many teeth are found in mouth.

No exoskeleton.