Class - Chondrichthyes Questions in English

(B) $\rightarrow$ Location: In males of $Chondrichthyes$ (cartilaginous fishes),claspers are modified structures found on the pelvic fins.
$\rightarrow$ Function: These structures are used as intromittent organs to transfer sperm into the female reproductive tract during copulation.

(B) The image shows a fish with a long,saw-like snout,which is characteristic of the genus $Pristis$,commonly known as the sawfish.
$Pristis$ belongs to the class $Chondrichthyes$ (cartilaginous fishes).
$Trygon$ is a stingray,$Scoliodon$ is a dogfish shark,and $Carcharodon$ is the great white shark.
Therefore,the correct option is $B$.

(D) The heart of fishes is $2$-chambered,consisting of one atrium (auricle) and one ventricle.
Unlike mammals,reptiles,and amphibians,which have a divided atrium (left and right auricles),the fish heart receives only deoxygenated blood,which is then pumped to the gills for oxygenation.
Therefore,the heart in fishes does not have separate left and right auricles.

(D) $Trygon$ (commonly known as the stingray) is a cartilaginous fish that belongs to the class $Chondrichthyes$.
It possesses a venomous poison sting,which is a modified dermal denticle located on its tail,used for defense.
$Labeo$ is a bony fish (class $Osteichthyes$).
$Myxine$ (hagfish) belongs to the class $Cyclostomata$.
$Clarias$ (catfish) is a bony fish (class $Osteichthyes$).

(A) Statement-$I$ is correct: In cartilaginous fishes (Class Chondrichthyes),the skin is tough and contains minute placoid scales. The teeth are modified placoid scales that are backwardly directed.
Statement-$II$ is correct: These fishes are primarily predators,and their jaws are very powerful to capture and hold prey.

(D) In the classification of $Chondrichthyes$ (cartilaginous fishes):
$1$. $Torpedo$ possesses electric organs to generate electricity.
$2$. $Trygon$ is known for its poisonous sting.
$3$. $Exocoetus$ is commonly known as the flying fish.
$4$. $Hippocampus$ is commonly known as the sea horse, whereas the saw fish is $Pristis$.
Therefore, the pair $Hippocampus : \text{Saw fish}$ is mismatched.

(C) Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes) are two classes of the phylum Chordata.
$1$. Chondrichthyes possess a cartilaginous endoskeleton, whereas Osteichthyes possess a bony endoskeleton.
$2$. Chondrichthyes lack an air bladder (swim bladder), which is present in Osteichthyes to regulate buoyancy.
$3$. Chondrichthyes have placoid scales, while Osteichthyes have cycloid or ctenoid scales.
$4$. Male Chondrichthyes possess pelvic fins with claspers, which are copulatory organs used for internal fertilization. These are absent in Osteichthyes.
$5$. Chondrichthyes have $5-7$ pairs of gills without an operculum (gill cover), whereas Osteichthyes have $4$ pairs of gills covered by an operculum.
Therefore, the presence of claspers is a distinguishing feature of Chondrichthyes.

(A) Cartilaginous fishes (Class $Chondrichthyes$) lack an air bladder (swim bladder), which is a gas-filled organ that provides buoyancy in bony fishes.
Because they lack this organ, they are denser than water and tend to sink if they stop swimming.
Therefore, they must swim constantly to maintain their position in the water column and prevent sinking.
Thus, both the Assertion and the Reason are true, and the Reason correctly explains the Assertion.