Class - Chondrichthyes Questions in English

(C) Statement $X$ describes the characteristic features of the class $Chondrichthyes$ (cartilaginous fishes),which include a streamlined,boat-shaped body and skin covered with placoid scales.
Statement $Y$ also describes the characteristics of the class $Chondrichthyes$,where the mouth is located ventrally and the jaws are powerful and toothed.
Since both statements describe the diagnostic features of the class $Chondrichthyes$,both statements are correct and belong to the same class.

(A) The class $Chondrichthyes$ includes marine animals with a streamlined body and a cartilaginous endoskeleton.
Sharks (e.g.,$Scoliodon$) belong to this class.
Since the endoskeleton is composed of cartilage,they are called cartilaginous fishes.
Therefore,both the statement $(S)$ and the reason $(R)$ are true,and the reason $(R)$ correctly explains the statement $(S)$.

(B) The class $Chondrichthyes$ (cartilaginous fishes) is characterized by the presence of a heterocercal caudal fin,where the vertebral column extends into the upper lobe of the tail,making it asymmetrical.
In contrast,the class $Osteichthyes$ (bony fishes) typically possesses a homocercal (symmetrical) caudal fin.
$Urochordata$ is a subphylum of $Chordata$ and does not belong to the class of fishes.
Therefore,the correct answer is $Chondrichthyes$.

(D) The animal kingdom is divided into various classes. The class $Chondrichthyes$ consists of cartilaginous fishes,meaning their endoskeleton is made entirely of cartilage.
Among the given options:
$1$. $Seahorse$ $(Hippocampus)$,$Catla$,and $Labeo$ belong to the class $Osteichthyes$ (bony fishes),which have a bony endoskeleton.
$2$. $Ray$ $fish$ $(Trygon)$ belongs to the class $Chondrichthyes$,which possesses a cartilaginous endoskeleton.
Therefore,the correct answer is $Ray$ $fish$.

(B) The class $Chondrichthyes$ (cartilaginous fishes) consists of animals that lack an exoskeleton. Their skin is covered with placoid scales,which are dermal in origin and not considered a true exoskeleton like the scales found in $Reptilia$ or the feathers in $Aves$. $Amphibia$ also generally lack an exoskeleton,but $Chondrichthyes$ is the classic example in this context regarding the absence of a protective external covering like scales or feathers.

(B) The animals belonging to the class $Chondrichthyes$ (cartilaginous fishes) possess an endoskeleton made entirely of cartilage.
Among the given options,$Ray-fish$ (e.g.,$Trygon$) belongs to the class $Chondrichthyes$.
$Ichthyophis$ is an amphibian,while $Catla$ and $Labeo$ are bony fishes belonging to the class $Osteichthyes$.

(B) Cartilaginous fishes belong to the class $Chondrichthyes$.
These fishes are characterized by a cartilaginous endoskeleton.
The skin of these fishes is tough and contains minute,tooth-like structures called $Placoid$ scales.
These scales are structurally similar to teeth,consisting of a central pulp cavity covered by dentine and an outer layer of enamel.
Therefore,the correct answer is $Placoid$ scales.

(A) The electric ray fish,belonging to the genus $Torpedo$,is a member of the class $Chondrichthyes$.
Members of the class $Chondrichthyes$ are characterized by having a cartilaginous endoskeleton.
Therefore,the electric ray is classified as a cartilaginous fish.

(B) true fish belongs to the class $Chondrichthyes$ (cartilaginous fishes) or $Osteichthyes$ (bony fishes).
$1$. Jellyfish is a $Cnidarian$,not a fish.
$2$. Ray fish (like $Stingray$) belongs to the class $Chondrichthyes$ and is a true fish.
$3$. Hagfish $(Myxine)$ belongs to the class $Cyclostomata$,which are jawless vertebrates,but they are often distinguished from 'true' fishes $(Gnathostomata)$.
$4$. Ichthyofish is not a standard biological name for a fish.
Among the given options,the Ray fish is a cartilaginous fish and is considered a true fish.

(B) The organisms belonging to the class $Chondrichthyes$ (cartilaginous fishes) possess a cartilaginous endoskeleton.
Among the given options,the shark belongs to the class $Chondrichthyes$.
Lamprey belongs to the class $Cyclostomata$ (which have a cartilaginous and fibrous endoskeleton,but the question specifically targets the cartilaginous nature of the shark in typical classification contexts).
Ray fish also belongs to $Chondrichthyes$,but sharks are the most representative example of cartilaginous fish.
Catla belongs to the class $Osteichthyes$ (bony fishes).
Therefore,the shark is the correct answer.

(A) The animals belonging to the class $Chondrichthyes$ (cartilaginous fishes),such as sharks,possess gill slits that are separate and not covered by an operculum (gill cover).
In contrast,members of the class $Osteichthyes$ (bony fishes),such as $Catla$,$Labeo$,and $Hippocampus$ (seahorse),possess four pairs of gills which are covered by an operculum on each side.
Therefore,the shark is the correct answer as it has open gill slits.

(A) In cartilaginous fishes (class $Chondrichthyes$),the caudal fin is heterocercal,meaning it is asymmetrical with the vertebral column extending into the upper lobe. This structure provides efficient propulsion and maneuverability in water.

(C) Sharks belong to the class $Chondrichthyes$ (cartilaginous fishes).
Their skin is characterized by the presence of $placoid$ scales.
These scales are structurally similar to teeth,consisting of a central pulp cavity surrounded by dentine and covered by an enamel-like substance.
$Cycloid$ and $ctenoid$ scales are typically found in bony fishes $(Osteichthyes)$,while $cosmoid$ scales are found in lungfishes and some fossil fishes.

(B) In the class $Chondrichthyes$,which includes cartilaginous fishes like sharks and rays,the mouth is located on the ventral side of the body. Specifically,in rays,the mouth is positioned on the $Antero-ventral$ side to facilitate feeding from the sea floor.

(A) The caudal fin is the tail fin of a fish.
In Chondrichthyes (cartilaginous fishes),such as the $Shark$,the caudal fin is heterocercal,meaning it is asymmetrical with the vertebral column extending into the upper lobe.
In contrast,Osteichthyes (bony fishes) like $Catla$,$Labeo$,and $Seahorse$ typically possess homocercal (symmetrical) caudal fins.

(C) Assertion $A$ is true because many shark species are indeed viviparous,meaning they give birth to live young.
Reason $R$ is false because sharks are cartilaginous fishes (Class $Chondrichthyes$),not mammals.
Mammary glands are a unique characteristic of mammals,which sharks do not possess.
Therefore,$A$ is true and $R$ is false.

(D) Fish scales are typically derived from the dermis,such as placoid,cycloid,and ctenoid scales.
Epidermal scales are characteristic of terrestrial vertebrates like reptiles (e.g.,snakes and lizards) and are not found in fish.
Therefore,the correct answer is $D$.

(A) true fish belongs to the class $Pisces$ (or $Chondrichthyes$/$Osteichthyes$).
$1$. $Dogfish$ $(Scoliodon)$ is a cartilaginous fish belonging to the class $Chondrichthyes$.
$2$. $Silverfish$ is an insect $(Arthropoda)$.
$3$. $Starfish$ is an echinoderm $(Echinodermata)$.
$4$. $Cuttlefish$ is a mollusk $(Mollusca)$.
Therefore,$Dogfish$ is the only true fish among the given options.

(B) Fish scales are classified based on their structure and composition.
Common types of fish scales include $Placoid$,$Cycloid$,$Ctenoid$,and $Ganoid$ scales.
$Placoid$ scales are typically found in cartilaginous fishes (Chondrichthyes).
$Cycloid$ and $Ctenoid$ scales are commonly found in bony fishes (Osteichthyes).
$Steroid$ is a type of lipid (hormone) and is not a structure associated with fish scales.

(D) The animals $Seahorse$ $(Hippocampus)$,$Labeo$ $(Rohu)$,and $Catla$ $(Catla)$ belong to the class $Osteichthyes$ (bony fishes).
$Shark$ $(Scoliodon)$ belongs to the class $Chondrichthyes$ (cartilaginous fishes).
Therefore,$Shark$ is the odd one out because it has a cartilaginous endoskeleton,while the others have a bony endoskeleton.

(A) The evolution of the heart shows a transition from simple to complex structures.
$1$. Cartilaginous fishes (Chondrichthyes) possess a two-chambered heart (one atrium and one ventricle),not a non-chambered heart.
$2$. Amphibians have a three-chambered heart (two atria and one ventricle).
$3$. Reptiles (except crocodiles) have a three-chambered heart with a partially divided ventricle.
$4$. Birds and mammals have a four-chambered heart (two atria and two ventricles).
Therefore,option $A$ is the incorrect statement.

(D) The group $Pisces$ (fishes) are aquatic organisms that possess gills for respiration,fins for locomotion,and scales covering their body for protection.
External pinnae (external ears) are a characteristic feature of the class $Mammalia$ (mammals),not $Pisces$.
Therefore,the correct answer is $D$.

(C) is the correct answer.
$1$. Phylum Chordata includes both jawless vertebrates (Agnatha) and jawed vertebrates (Gnathostomata). Therefore,not all chordates possess jaws.
$2$. Most reptiles have a $3$-chambered heart with one incompletely divided ventricle,but crocodiles have a $4$-chambered heart.
$3$. Class Chondrichthyes consists of cartilaginous fishes,which always possess a cartilaginous endoskeleton.
$4$. While most mammals are viviparous,some like the duck-billed platypus and spiny anteater are oviparous.

(B) $Torpedo$ is a bottom-living marine cartilaginous fish that can discharge electricity,which is sufficient to stun prey such as small fishes.
$A$ pair of electric organs are situated on the dorsal side of the trunk region.
In fact,these electric organs are modified lateral muscle plates innervated by the cranial nerves.

(D) : Sharks and dogfishes possess a cylindrical body shape. In contrast,skates and rays have their pectoral fins fused with the body,giving them a flattened,wing-like appearance that is not distinctly separated from the main body.

(C) The correct option is $C$.
$A$: Reptiles like crocodiles have a $4$-chambered heart,so this is not true for all reptiles.
$B$: Chordates include Agnatha (jawless vertebrates),so this is not true for all chordates.
$C$: All members of the class Chondrichthyes are characterized by a cartilaginous endoskeleton. This is a defining feature without exception.
$D$: Mammals like Ornithorhynchus (platypus) and Tachyglossus (echidna) are oviparous (egg-laying),so this is not true for all mammals.

(C) Vertebrates are chordates that possess a vertebral column.
$A$. $Branchiostoma$ (Amphioxus) is a cephalochordate,not a vertebrate.
$B$. $Ascidia$ is a urochordate (tunicate),not a vertebrate.
$C$. $Scoliodon$ (Dogfish) belongs to the class Chondrichthyes under the subphylum Vertebrata.
$D$. $Salpa$ is a urochordate,not a vertebrate.
Therefore,$Scoliodon$ is the correct answer.

(B) The electric organ is a specialized structure found in certain fish species that allows them to generate electric fields for defense,navigation,or communication.
Among the given options,$Torpedo$ (also known as the electric ray) is well-known for possessing paired electric organs located on either side of its head.
These organs are modified muscle tissues capable of producing significant electric shocks.
$Trygon$ (stingray) possesses a venomous spine,$Catla$ is a bony fish,and $Flying$ $fish$ $(Exocoetus)$ is known for its ability to glide,but none of these possess specialized electric organs.

(D) $Trygon$ belongs to the class $Chondrichthyes$ (cartilaginous fishes).
$1$. Like all fishes,they have a two-chambered heart consisting of one atrium and one ventricle.
$2$. In $Chondrichthyes$,the pelvic fins of males bear special copulatory organs called claspers.
$3$. Their skin is tough and contains minute placoid scales.
Since all these statements are correct,the correct option is $D$.

(C) The correct matches are as follows:
$(1)$ $Scoliodon$ is commonly known as the $Dog$ $fish$.
$(2)$ $Pristis$ is commonly known as the $Saw$ $fish$.
$(3)$ $Carcharodon$ is commonly known as the $Great$ $white$ $shark$.
$(4)$ $Trygon$ is commonly known as the $Sting$ $ray$.
Therefore,the correct matching sequence is $1-r, 2-p, 3-s, 4-q$.

(D) The figure shows a sawfish,which is scientifically known as $Pristis$. It is a cartilaginous fish belonging to the class Chondrichthyes. The characteristic feature of this organism is its long,saw-like rostrum.

(B) The class $Chondrichthyes$ (cartilaginous fishes) possesses a $2$-chambered heart.
This heart consists of one auricle (atrium) and one ventricle.
It is a venous heart,meaning it pumps only deoxygenated blood to the gills for oxygenation.

(A) Claspers are specialized copulatory organs found in the pelvic fins of male cartilaginous fishes (Chondrichthyes).
Among the given options,$Pristis$ (Sawfish) belongs to the class Chondrichthyes.
$Petromyzon$ (Lamprey) and Hagfish belong to the class Cyclostomata,which lack paired fins and claspers.
Therefore,the correct answer is $Pristis$.

(C) Let us analyze each option:
$A$: Chordata includes Agnatha (jawless vertebrates like lampreys),so this is not true for all chordates.
$B$: Reptiles like crocodiles have a $4$-chambered heart,so this is not true for all reptiles.
$C$: Chondrichthyes are characterized by a cartilaginous endoskeleton,which is a defining feature of this class.
$D$: While most mammals are viviparous,monotremes (like the platypus) are oviparous,so this is not true for all mammals.
Therefore,the correct option is $C$.

(D) $1$. In $Ascaris$ (roundworm),the male is smaller than the female and has a curved posterior end,while the female is longer and has a straight posterior end. Thus,option $A$ is incorrect.
$2$. In frogs,the male can be identified by the presence of a copulatory pad (nuptial pad) on the first digit of the forelimb (not hind limb). Thus,option $B$ is incorrect.
$3$. In cockroaches,the male possesses anal styles,while the female does not. Thus,option $C$ is incorrect.
$4$. In male sharks (cartilaginous fish),the pelvic fins bear specialized copulatory organs called claspers,which are used to transfer sperm to the female. This is a correct diagnostic feature for identifying the sex of a shark. Thus,option $D$ is correct.

(C) Let's analyze the options:
$A$. Reptiles: Most reptiles have a three-chambered heart,but crocodiles have a four-chambered heart. Thus,this is not an exception-free statement.
$B$. Chordates: Not all chordates have jaws (e.g.,Agnatha are jawless vertebrates). Thus,this is incorrect.
$C$. Chondrichthyes: This class is defined by having a cartilaginous endoskeleton. This is a universal characteristic for all members of this class.
$D$. Mammals: While most mammals are viviparous,monotremes (like the platypus) are oviparous (egg-laying). Thus,this is not an exception-free statement.
Therefore,the correct option is $C$.

(B) The cartilaginous fish $Torpedo$,commonly known as the electric ray,possesses specialized electric organs derived from modified muscle tissue. These organs are capable of generating a powerful electric discharge used for both defense and capturing prey. $Pristis$ is the sawfish,$Trygon$ is the stingray,and $Scoliodon$ is the dogfish shark; none of these produce electric currents.

(N/A) The class $Chondrichthyes$ (cartilaginous fishes) exhibits the following characteristics:
$1$. They are marine animals with a streamlined body and have a cartilaginous endoskeleton.
$2$. The mouth is located ventrally.
$3$. Notochord is persistent throughout life.
$4$. Gill slits are separate and without an operculum (gill cover).
$5$. The skin is tough,containing minute placoid scales.
$6$. Teeth are modified placoid scales which are backwardly directed.
$7$. Their jaws are very powerful.
$8$. Due to the absence of an air bladder,they have to swim constantly to avoid sinking.
$9$. The heart is two-chambered (one auricle and one ventricle).
$10$. Some of them have electric organs (e.g.,$Torpedo$) and some possess poison stings (e.g.,$Trygon$).
$11$. They are cold-blooded (poikilothermous) animals.
$12$. Sexes are separate. In males,pelvic fins bear claspers.
$13$. Fertilization is internal and many of them are viviparous.

(B) The adaptive features of $Chondrichthyes$ are as follows:
$1$. They are cartilaginous fishes with a streamlined body.
$2$. They lack an air bladder,which is why they must swim constantly to avoid sinking.
$3$. They possess placoid scales and their jaws are very powerful.
$4$. Some members possess electric organs (e.g.,$Torpedo$) or poison stings (e.g.,$Trygon$).

(N/A) $\rightarrow$ Chondrichthyes are marine animals with a streamlined body and a cartilaginous endoskeleton.
$\rightarrow$ The mouth is located ventrally.
$\rightarrow$ The notochord is persistent throughout life.
$\rightarrow$ Gill slits are separate and without an operculum (gill cover).
$\rightarrow$ The skin is tough, containing minute placoid scales.
$\rightarrow$ Teeth are modified placoid scales which are backwardly directed.
$\rightarrow$ Their jaws are very powerful.
$\rightarrow$ These animals are predaceous.
$\rightarrow$ Due to the absence of an air bladder, they have to swim constantly to avoid sinking.
$\rightarrow$ The heart is two-chambered (one auricle and one ventricle).
$\rightarrow$ Some of them have electric organs (e.g., Torpedo) and some possess a poison sting (e.g., Trygon).
$\rightarrow$ They are cold-blooded (poikilothermous) animals, i.e., they lack the capacity to regulate their body temperature.
$\rightarrow$ Sexes are separate.
$\rightarrow$ In males, pelvic fins bear claspers.
$\rightarrow$ Examples: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray).

(A) The $Coelacanth$ is a lobe-finned fish that was believed to have gone extinct approximately $65$ million years ago. However,in $1938$,a living specimen was caught off the coast of South Africa. This discovery provided significant evidence for the evolutionary transition from aquatic to terrestrial life,as $Coelacanths$ are considered to be the ancestors of amphibians.

(D) $Chondrichthyes$ lack swim bladders,which help in maintaining buoyancy; therefore,they must swim constantly to avoid sinking.
$Chondrichthyes$ are ureotelic animals,meaning they excrete urea as their primary nitrogenous waste.
Since both statements $(a)$ and $(b)$ are incorrect,the correct option is $(d)$.

(A) $Chondrichthyes$ are cartilaginous fishes.
In $Chondrichthyes$,teeth are modified placoid scales which are backwardly directed.

(A) Torpedo (electric ray) is a carnivorous fish. It stuns or kills its prey with an electric shock generated by its specialized electric organs. These electric organs are modified muscles that can produce an electric discharge ranging from $8$ volts to $220$ volts.

(B) Cartilaginous fishes (class $Chondrichthyes$) possess $Placoid$ scales on their skin,which are backwardly directed.
In contrast,$Cycloid$,$Ctenoid$,and $Ganoid$ scales are typically observed in bony fishes (class $Osteichthyes$).

(A) Ampullae of Lorenzini are specialized sensory organs found in cartilaginous fishes,such as sharks and rays. They are located in the snout and act as electroreceptors and thermoreceptors,allowing these animals to detect changes in temperature and weak electric fields in their aquatic environment.

(C) In $Torpedo$ (electric ray),the electric organs are specialized structures derived from modified branchial muscles. These organs are located on the dorsal side of the head,specifically positioned between the gills and the eyes.

(C) Sharks belong to the class $Chondrichthyes$ (cartilaginous fishes).
$a$. The skin is tough and covered with placoid scales: This is true.
$b$. They possess a swim bladder which regulates buoyancy: This is false. Cartilaginous fishes lack a swim bladder,which is why they must swim continuously to avoid sinking.
$c$. The tail of shark is heterocercal: This is true.
$d$. Ampulla of Lorenzini present in the snout of shark is a thermoreceptor: This is true. These organs are sensitive to temperature and electrical fields.
$e$. It has five pairs of gill slits covered by operculum: This is false. In $Chondrichthyes$,gill slits are separate and without an operculum (gill cover).
Therefore,statements $b$ and $e$ are not true.

(B) Statement $a$ is true: Dermal scales in fishes form the exoskeleton.
Statement $b$ is true: Cycloid and ctenoid scales exhibit growth rings (circuli) that help in age determination.
Statement $c$ is false: Some fish species do shed their scales,or scales may be lost due to injury and regenerated.
Statement $d$ is true: Elasmobranchs (cartilaginous fishes) possess placoid scales.
Statement $e$ is false: The development of a placoid scale is structurally and developmentally similar to that of a vertebrate tooth,as both consist of a pulp cavity,dentine,and an enamel-like covering (vitrodentine).

(C) In cartilaginous fishes (Chondrichthyes),placoid scales are modified into teeth which are backwardly directed.