Question

How the animals in vertebrates are classified in further subgroups. Explain.

Answer 1

Hint: The subphylum vertebrata is divided into two subgroups Agnatha (which lacks jaws) and Gnathostomata (which bears jaw).

Complete answer:
The vertebrata is a subphylum of the phylum Chordata.
Further, the phylum chordata is divided into three subphyla namely Urochordata, Cephalochordata and Vertebrata.

Vertebrata are divided into Agnatha and Gnathostomata.
- Agnatha superclass consists of class cyclostomata in which the organisms do not bear jaws, Hagfishes and Lampreys are its good examples.
- Gnathostomata consists of all organisms that bear true jaws. It is divided into superclass Pisces and Tetrapoda which are again divided into subgroups.

1. Pisces:
   These are fish characterized by the presence of scales/plates. These are cold blooded organisms with two chambered hearts and are oviparous.
   Some of these have skeletons made of cartilage (classified as chondrichthyes) such as shark, dog fish and stingrays. Others have their skeleton made of both bones and cartilage (named as osteichthyes) like flying fish, seahorse.

2. Tetrapoda:
   These organisms bear limbs, its classes are listed below:
   a) Amphibians – These are both aquatic as well as terrestrial like frog, toad, tree frog, and salamander.
   b) Reptilia- These have creeping/crawling mode of locomotion. Example: tortoise, garden lizard, crocodile and snakes etc.
   c) Aves- These have presence of pneumatic bones for ease in flight such as crow, ostrich, pigeon, etc.
   d) Mammalia- They have the presence of mammary glands to nourish their young ones. These include kangaroos, dolphins, blue whales and humans.

Note: All the organisms in the above classes /sub groups are divided on the basis of their key features resembling the group, not only on their morphological features.