Vertebrate Classification

                                                             

     
                                                              Classes of Vertebrates

Class - Cyclostomata

The living members of this class are all ectoparasites on some fishes. They have a elongated body. They bear 6-15 pairs of gills through which they respire. The mouth of the cyclostomes is sucking circular mouth without jaws. They do not have body scales and paired fins. The vertebral column and the cranium is cartilaginous. Circulation is closed type. These are marines organisms but  they migrate to fresh water for spawning. After metamorphosis their larvae returns to the ocean.

Example: Petromyzon (Lamprey), and Myxine (Hagfish).

Class - Chondrichthyes

These organisms are marine and have streamlined body. The endoskeleton is cartilaginous. Mouth is located ventrally and the notochord is present throughout life. The gills are separate and are not covered by the operculum. The skin contains minute placoid scales. The placoid scales are modified as teeth and the jaws are powerful. They are predaceous animals. Air bladder is absent in these animals, hence, they have to swim constantly to avoid shrinking.

Example: Scolidon, Pristis, Trygon.



Class - Osteichthyes

This class includes animals that are both marine and fresh water fishes with bony endoskeleton. Their body is streamlined. Mouth is terminal in position. The gills are covered with operculum on each side and are in four pairs.The skin is covered by ctenoid/cycloid scales. Air bladder is present, it regulates buoyancy. Two-chambered heart is present, with one auricle and one ventricle. They are poikilothermic animals. The sexes are separate, fertilization takes place externally. Most of them are oviparous animals and development is direct, with no larval stages.

Example: Hippocampus, Clarias.

Class - Amphibia

The name Amphibia indicates - from Greek, Amphi meaning dual and bios meaning life. 

Ampibians can live both in aquatic and terrestrial habitats. These animals have two pairs of limbs. Body is divisible into head and trunk and tail is present in some animals. The skin of these animals are scaleless and moist. The eyes have eyelids, and the ears are represented by a tympanum. Cloaca is a opening to the exterior, it is a common chamber for the alimentary canal, urinary and reproductive tracts.Gills, lungs and skin aids in respiration. Heart is three-chambered. They are cold-blooded animals. Sexes are separate, fertilization is external. They are oviparous animals and development is indirect. 

Example: Toad, frog, salamander.

Class - Reptilia

In Latin repere or reptum means to creep or crawl, hence, the class name refers to locomotion that is of creeping or crawling mode. 

These animals are mostly terrestrial and their body is covered dry and cornified skin, epidermal scales or scutes. External ear opening is absent, tympanum represents the ear. Limbs, if present are of two pairs. Usually heart is three-chambered, but is four chambered in crocodiles. They are poilkilothermic animals. Some animals like the snake and the lizards shed their skin. Sexes are separate, internal fertilization takes place. They are oviparous and development is direct. 

Example: Turtle, Chameleon, crocodile.

Class - Aves

Most of the members can fly, except the flightless birds. The characteristic feature of birds is the presence of feathers. The forelimbs are modified as wings. The hind limbs are modified for walking, swimming or clasping and generally have scales. The skin is dry and does not have glands, except a oil gland at the base of the tail. Endoskeleton is bony, and the bones are hollow with air cavities known as pneumatic bones. Heart is four-chambered completely. They are warm-blooded animals. Lungs are the organs of respiration. Sexes are separate, fertilization is internal. They are oviparous animals and development is direct. 

Example: Crow, Pigeon, Parrot etc.

Class - Mammalia

Mammals are present in almost all habitats - polar ice caps, deserts, mountains, forests, and grasslands.The unique characteristic of the class mammalia is the presence of milk producing glands (mammary glands), by which the young ones are nourished. The limbs are of two pairs. The skin is covered with hairs. External ear 'pinna' is present. Heart is four-chambered and they are homeothermic animals. Respiration is through lungs. Sexes are separate and fertilization is internal. They viviparous animals, with direct development. 

Example: Kangaroo, Tiger, Lion, Platypus etc.