Vertebrata, Biology

VERTEBRATA

It is divided into two parts -        1. Agnetha                    2. Gnetha

S.No.

Character

Agnetha

Gnetha

 

1

 

True Jaws

 

Absent

 

Present

2

Paired apendages

Absent

Present

3

Semi circular canal in internal ear

2

3

4

Nostril

1

2

 

1.

AGNETHA

 

Agnetha is divided into two parts -

1. Ostracodermi

2. Cyclostomata

(I)      OSTRACODERMI

  • First vertebrate. Greatly armoured. All fossils.

EXAMPLES -   Cephalospis

(II)     CYCLOSTOMATA

Body eel like. Mouth sucker type.  Ectoparasite.

Gills 5-16 pairs. Pineal eye present.

Unicellular shin glands present.

Scales absent. Sanguivorous.

On tongue horny teeth present.

EXAMPLES -

1.       Petromyzon                                - lamprey, lampredin present, 7 pairs gills, larva is ammocoet for seven years, living fossil

2.       Myxine                                        - Hag fish, lips as of old lady, bisexual, development direct

 

Note :- Before pisces & after cyclostomata placodermi is a group of extinct fishes (jawed).

These are most primitive fishes. Example- climatius

2.      GNETHA

Gnetha is divided into 5 classes -

1. Pisces

2. Amphibia

3. Reptilia

4. Aves

5. Mammalia

Posted Date: 10/1/2012 1:46:08 AM | Location : United States







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