● `color{Brown}"Habitat"`: They are marine animals.

● `color{Brown}"Body"`:
`star` They have `color{Violet}"streamlined body"`

`star` The skin is tough, containing minute `color{Violet}"placoid"` ( plate like) scales.



`star` Teeth are `color{Violet}"modified placoid scales"` which are backwardly directed. Their jaws are very powerful.



● `color{Brown}"Location of mouth"` : Mouth is located `color{Violet}"ventrally"`.

● They are cold-blooded (`color{Violet}"poikilothermous"`) animals.

● These animals are `color{Violet}"predaceous"`.

● `color{Brown}"Skeletal system"`:

`star` They have `color{Violet}"cartilaginous endoskeleton"`.

`star` Notochord is `color{Violet}"persistent"` throughout life.

● `color{Brown}"Respiratory system"`:

`star` Gill slits are `color{Violet}"separate"` and without operculum (gill cover).

`star` Due to the absence of air bladder, they have to `color{Violet}"swim constantly"` to avoid sinking.



● `color{Brown}"Circulatory system"` : Heart is `color{Violet}"two-chambered"` (one auricle and one ventricle).

● `color{Brown}"Characteristic organs"` : Some of them have `color{Violet}"electric organs"` (e.g., Torpedo) and some possess `color{Violet}"poison sting"` (e.g., Trygon).

●Sexes are `color{Violet}"separate"`. In males pelvic fins bear `color{Violet}"claspers"`.



●They have `color{Violet}"internal fertilisation"` and many of them are `color{Violet}"viviparous"`.

● `color{Brown}"Examples"`: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray).

● `color{Brown}"Habitat"`: It includes both marine and fresh water fishes.

● `color{Brown}"Body"`:

`star` They have `color{Violet}"streamlined"` body

`star` Skin is covered with `color{Violet}"cycloid/ctenoid scales"`.

● `color{Brown}"Location of mouth"` : Mouth is mostly `color{Violet}"terminal"`

● They are cold-blooded( `color{Violet}"poikilothermic"` animals) animals.

● `color{Brown}"Respiratory system"`:
`star` They have `color{Violet}"four pairs of gills"` which are covered by an operculum on each side.

`star` `color{Violet}"Air bladder"` is present which regulates buoyancy.

● `color{Brown}"Circulatory system"`: Heart is `color{Violet}"two-chambered"` (one auricle and one ventricle).

● They are `color{Violet}"cold-blooded"` animals.

● Sexes are `color{Violet}"separate"`.

● Fertilisation is usually `color{Violet}"external"`.

● They are mostly `color{Violet}"oviparous"` and development is `color{Violet}"direct"`.

● `color{Brown}"Examples"`: Marine – Exocoetus (Flying fish), Hippocampus (Sea horse); Freshwater – Labeo (Rohu), Catla (Katla), Clarias (Magur); Aquarium – Betta (Fighting fish), Pterophyllum (Angel fish).