Q. 9

Give the characteristic features of the following citing one example of each

a. Chondrichthyes and ostichthyes

b. Urochordata and cephalochordate

Answer :

a. Chondrichthyes and ostichthyes


Chodrichthyes :


• Their habitat is mainly marine and their body is streamlined. They have cartilaginous endoskeleton.


• Mouth is ventrally (near the front of the body) located.


• Notochord is persistent throughout the life.


• The air bladder is absent due to which they have to swim constantly to prevent sinking.


• They have tough skin, containing placoid scales. The teeth are modified placoid scales directed backwards.


• Heart is 2-chambered and they are cold blooded.


• Gill slits are separated and without operculum (cover for gills)


• Examples – Scoliodon, Pristis , Trygon


Ostichthyes


• The habitat is both marine as well as freshwater and they have a streamlined body. The endoskeleton is bony.


• Mouth is mostly terminal.


• Air bladder is present which gives buoyancy.


• There are 4 pairs of gills with operculum present.


• They are cold blooded.


• Heart has 2 chambers (1 auricle and 1 ventricle).


• Skin is covered with cycloid/ctenoid scales.


• Examples – Marinee : Hippocampus (Sea horse), Freshwater : Labeo (Rohu), Aquarium : Betta (Fighting fish)


b) Urochordata and cephalochordata


• Phylum chordata is divided into three categories – urochordata, cephalochordata and vertebrate.


• Urchordata and cephalochordate are often referred to as protochordates.


• They are exclusively marine.


• In urochordates, the notochord is present only in larval tail but in cephalochordates, notochord extends from head to tail region and is persistent throughout the life.


• Examples – Urochordates: Ascidia , Salpa , Cephalochordates : Branchiostoma.


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