Phylum: Chordata (Part – II)

The subphylum vertebrata has 2 super classes Agnatha and Gnathostomata.

Agnatha: Jawless vertebrates, mouth does not possess jaws hence named Agnatha. They are cold blooded and further divided into following classes;

Class: Ostracodermi: primitive, extinct group of Agnatha, Paleozoic and world’s first vertebrates called Ostracoderms.

Class: Cyclostomata: Body cell shaped, without scales, jaws and lateral fins. Mouth rounded, gills 5-16 pairs and are parasites and scavengers. Example: Lampreys (Petromyzon) and Hagfishes (Myxine).

Gnathostomata: Jawed vertebrates having true jaws and paired limbs. Paired nostrils are present and divided into two super classes; Pisces and Tetrapoda.

Superclass: Pisces: True fishes (aquatic), body bears paired, respired by gills and cold blooded. They possess scaly skin. Pisces divided into three classes;

Class: Placodermi: includes the earliest fossil fishes which lived in fresh water. Primitive jaws with teeth present. Skeleton was bony. Example: Climatius, Dinichthys.

Class: Chondrichthyes: marine fishes having cartilaginous endoskeleton. Five to seven pairs of gills. Gill-slits not covered by operculum. Male fishes have pelvic claspers. Example: Scoliodon, Chimera.

Class: Osteichthyes: Endoskeleton bony, skin having various types scales. Gill slits covered by operculum. Male fishes without claspers, Example: Labeo (Rohu), Protopterus (Lung fish), Hippocampus (Sea horse).

Superclass: Tetrapoda: Land vertebrates with two pairs of pentadactyl limbs; have cornified skin and lungs. Tetrapoda is divided into four classes;

Class: Amphibia: Adults are amphibious and respire by lungs. Breathe by gills, skin moist, glandular and with no external scales. Heart 3-chambered and cold blooded. Example: Rana (Frog), Bufo (Toad).

Class: Reptilia: terrestrial, dry skin and covered by ectodermal horny scales or bony plates. Heart incompletely 4-chambered and cold blooded. Example: Hemidactylus (lizard), snakes, turtles, Crocodiles.

Class: Aves: Body covered with feathers. Forelimbs modified into wings. No teeth in beak. Heart 4 chambered. Warm blooded. Example: Ostrich, Columba (Pigeon), crow, male tufted duck, white stork.

Class: Mammalia: body covered by hair. Skin glandular, Mammary glands present and in females, mammary glands secrete milk for suckling the young. Heart 4 chambered warm blooded. Example: Echidna (Spiny anteater), Macropus (Kangaroo), Humans, Whale, Elephant, tiger, cat, bat, etc.

Explore NIOS Notes