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  4. In class-Chondrichthyes (1) notochord is persistent through life (2) gill slits are separate and without operculum (3) skin is tough, containing minute placoid scales (4) tympanum represents ear

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Q. In class-Chondrichthyes
(1) notochord is persistent through life
(2) gill slits are separate and without operculum
(3) skin is tough, containing minute placoid scales
(4) tympanum represents ear

BHUBHU 2010

Solution:

Chondrichthyes are marine animals with streamlined body and have cartilaginous endoskeleton. Mouth is ventrally located. Notochord is persistent throughout life. Gill slits are separate and without operculum (gill cover). The skin is tough, containing minute placoid scales. Teeth are modified placoid scales which are backwardly directed They are poikilothermic animals. Heart is two chambered and some of them have electric organs and some possess poison sting (Trygon). Example?Scoliodon, Priscis, Carcharodon, Trygon.