Tag: diversity in living world

• Agnatha is a superclass of jawless fish i.e these animals have no jaws.
• They come under the phylum chordata, subphylum vertebrata and includes the Cyclostomes and extinct Ostracoderm species.
• Placodermi is a class of armoured prehistoric fish having plated skin belonging to the superclass Gnathostomata (having jaws).
  
• Chondrichthyes is a class which contains cartilaginous fishes and belong to the superclass Gnathostomata.
  
• So the correct answer is 'Placodermi and Chondrichthyes'.

• Cyclostomata is a group of jawless living fishes which belong to the superclass Agnatha.
• Eg- the lampreys and hagfishes.
  
• The name Cyclostomata means circular mouths.
  

Cephalochordates are a group of organisms in which the notochord extends from head to tail region and is persistent throughout their life. Agnatha is a group of vertebrates that lacks jaw and notochord is present in both larvae and adult forms. While in Gnathostomata (jawed vertebrates) notochord is replaced by a vertebral column in adults.

• Phylum Chordata can be divided into two categories:-

Agnatha is a superclass of jawless fishes in the phylum Chordata. These are ectothermic, meaning they do not regulate their own body temperature. They show slow metabolism in cold water. They do not have a proper stomach rather they have a long homogenous gut. They are lowest grade vertebrates. The notochord is persistent in them. 

The sea lamprey (Petromyzon marinus) is a parasitic lamprey found in the northern Atlantic Ocean along shores of Europe and North America, in the western Mediterranean sea and in the shores of the Great Lakes. It belongs to superclass Agnatha (It is a superclass of jawless fishes). It is brown, gray, or black on its back and white or gray on the underside. The lamprey uses its suction cup-like mouth to attach itself to the skin of a fish and rasps away tissue with its sharp, probing tongue and keratinized teeth.

Petromyzen or Lamprey is a living fossil. The sea lamprey lacks bony teeth and jaws. It has an oral armament of conical teeth made of keratin. The lamprey even has teeth on its tongue. The oral apparatus of the adult lamprey is a sucking disk lined with whorls of over 100 of these teeth. 

Cyclostomata is a group of chordates that comprises the living jawless fishes - the lampreys and hagfishes. These fishes are a parasite as well as scavengers. The body is long, then tubular and tail is flat. They are also known as false fish.