Class - Chondrichthyes Questions in English

(D) Polymorphism is a phenomenon where an organism exists in more than one morphological form within the same species.
In the phylum $Cnidaria$,specifically in the class $Hydrozoa$,organisms like $Physalia$ (Portuguese man-of-war) and $Obelia$ exhibit polymorphism.
They exist in different forms such as polyps (sessile) and medusae (free-swimming) to perform different functions like feeding,reproduction,and defense.
Therefore,the correct answer is $Hydrozoa$.

(B) In the class $Ophiuroidea$,the ambulacral grooves are either absent or completely covered by the ossicles. This is a characteristic feature that distinguishes them from other classes like $Asteroidea$,where open ambulacral grooves are present.

(B) On the basis of the presence or absence of jaws,the subphylum Vertebrata is classified into two divisions: Agnatha (jawless) and Gnathostomata (jawed).
$Agnatha$ includes primitive vertebrates like $Petromyzon$ (lamprey) which lack true jaws.
$Gnathostomata$ includes all vertebrates that possess true jaws,such as $Fish$,amphibians,reptiles,birds,and mammals.
Therefore,among the given options,$Fish$ belong to the division $Gnathostomata$ and possess jaws.

(A) The lateral line system is a sensory system found in fishes.
It is used to detect movement,vibration,and pressure gradients in the surrounding water.
This system helps the fish in navigation,schooling,and perceiving the distance of surrounding objects,which is essential for swimming.

(B) The correct answer is $(b)$ Dog fish.
Cartilaginous fishes belong to the class $Chondrichthyes$.
These fishes have a cartilaginous endoskeleton.
$Scoliodon$ (commonly known as Dog fish) is a classic example of a cartilaginous fish.
Silver fish is an insect,Cray fish is a crustacean,and Star fish is an echinoderm.

(A) The class $Chondrichthyes$ (which includes $Elasmobranchs$ like sharks and rays) is characterized by a cartilaginous endoskeleton.
$Dipnoi$ (lungfishes) and other bony fishes belong to the class $Osteichthyes$,which possess a bony endoskeleton.
$Mollusca$ is a phylum of invertebrates that typically have a soft body,often protected by a calcareous shell,but they do not possess an endoskeleton made of cartilage.

(D) . $Torpedo$ (also known as the electric ray) possesses specialized electric organs. These organs are highly modified masses of muscle cells capable of generating electric discharges for defense and prey capture.

(A) true fish belongs to the class $Pisces$ (or $Chondrichthyes$ and $Osteichthyes$).
$Dogfish$ $(Scoliodon)$ is a cartilaginous fish belonging to the class $Chondrichthyes$.
$Jellyfish$ is a $Cnidarian$,$Cuttlefish$ is a $Mollusc$,and $Silverfish$ is an $Arthropod$ (insect).
Therefore,$Dogfish$ is the only true fish among the given options.

(B) Elasmobranchs are a subclass of cartilaginous fishes that include sharks,rays,and skates.
These organisms are almost exclusively found in marine environments.
They possess specialized physiological adaptations to survive in high-salinity water,making them marine water forms.

(C) $Pristis$,commonly known as the sawfish,belongs to the class $Chondrichthyes$ (cartilaginous fishes).
Within this class,it is classified under the subclass $Elasmobranchii$,which includes sharks,rays,and skates.
$Dipnoi$ refers to lungfishes,$Teleostomi$ includes bony fishes,and $Holocephali$ includes chimaeras.

(A) Pharyngeal gill slits are a characteristic feature of the phylum Chordata.
Among the given options,the shark belongs to the class Chondrichthyes (cartilaginous fishes) under the phylum Chordata.
Sharks possess $5$ to $7$ pairs of gill slits that open directly to the exterior without an operculum.
Crayfish,cuttlefish,and starfish are non-chordates (invertebrates) and do not possess pharyngeal gill slits.

(A) . Dog fish (also known as $Scoliodon$) is a true fish belonging to the class $Chondrichthyes$.
$B$. Silver fish is an insect belonging to the phylum $Arthropoda$.
$C$. Star fish is an echinoderm belonging to the phylum $Echinodermata$.
$D$. Whale is a marine mammal belonging to the class $Mammalia$.
Therefore,the correct answer is $A$.

(B) Cartilaginous fishes, belonging to the class $Chondrichthyes$, possess several distinct characteristics.
$1$. Their mouth is located ventrally (Ventral mouth).
$2$. They have a cartilaginous endoskeleton.
$3$. They possess a heterocercal tail fin.
$4$. They lack an operculum (gill cover) and have $5-7$ pairs of gill slits.
Therefore, the presence of a ventral mouth is a key characteristic of this group.

(B) The heart of fishes is two-chambered,consisting of one auricle (atrium) and one ventricle. It pumps deoxygenated blood to the gills for oxygenation,which then circulates to the rest of the body.

(B) Fishes,amphibians,and reptiles are unable to maintain a constant body temperature. Therefore,they are called poikilothermic or cold-blooded animals.

(B) The correct answer is $B$. Fishes possess a $2$-chambered heart consisting of one auricle and one ventricle. This heart is known as a venous heart because it receives only deoxygenated (venous) blood and pumps it to the gills for oxygenation (purification).

(A) Gnathostomata is a superclass of vertebrates that possess jaws. Among the given options,$Fish$ (which includes both Chondrichthyes and Osteichthyes) are the earliest vertebrates to evolve jaws. Therefore,they are considered the first Gnathostomes in evolutionary history.

(A) The heart of a shark (a cartilaginous fish) is two-chambered,consisting of one atrium and one ventricle. It receives deoxygenated blood from the body and pumps it to the gills for oxygenation. Therefore,the heart only pumps deoxygenated blood. In contrast,whales are mammals (four-chambered heart),while frogs and lizards are amphibians and reptiles,respectively,which have three-chambered hearts that pump mixed blood.

(C) The 'Maltese cross' is a characteristic feature found in the vertebrae of sharks. Specifically,the centrum of the shark's vertebra is amphicoelous and is supported by four wedges of calcified fibrocartilage,which,when viewed in cross-section,resemble a 'Maltese cross'.

(A) The term $Mermaid's$ $purse$ is a common name used for the leathery egg cases or egg capsules laid by certain oviparous sharks,skates,and chimaeras.
These capsules protect the developing embryo and are often found washed up on beaches.

(B) The $Synanceia$ $horrida$,commonly known as the $Stone$ $fish$,is considered the most venomous fish in the world.
It possesses sharp spines on its dorsal fin that can inject a potent neurotoxin into its prey or predators.
This toxin causes extreme pain,tissue necrosis,and can be fatal to humans if not treated immediately.

(A) The Ampulla of Lorenzini in fishes is a specialized sensory organ known as a thermoreceptor (specifically an electroreceptor that is sensitive to temperature and electric fields).
It is primarily found in the snout region of cartilaginous fishes like sharks and rays.
These organs help the fish detect changes in the environment,including temperature gradients and weak electric fields generated by prey.

(A) Anadromous fishes are those that spend most of their adult lives in the sea but migrate to freshwater rivers or streams to spawn (breed).
Examples include $Salmon$ and $Lamprey$.
Therefore,the correct movement is from sea to freshwater.

(A) Cartilaginous fishes (Class $Chondrichthyes$) are characterized by a cartilaginous endoskeleton. $A$ key distinguishing feature of these fishes is the absence of an $operculum$ (gill cover) over their gill slits. Instead,they possess $5-7$ pairs of separate gill slits that open directly to the exterior. While they do possess placoid scales,pelvic fins,and gill slits,the operculum is absent.

(D) Viviparous animals are those that give birth to live young ones rather than laying eggs.
Among the given options,sharks (specifically many species of Chondrichthyes) exhibit viviparity or ovoviviparity,where the embryos develop inside the mother's body.
Bony fish,lung fish,and frogs are primarily oviparous,meaning they lay eggs in the external environment for development.

(B) $Echeneis$ is commonly known as the sucker fish. Its upper surface bears a large,flat,oval adhesive disc or sucker. This sucker represents a modified anterior dorsal fin,which allows the fish to attach itself to larger marine animals like sharks or turtles for transport and protection.

(A) Claspers are specialized intromittent organs located on the pelvic fins of male cartilaginous fishes (Chondrichthyes),such as sharks and rays,used to facilitate internal fertilization.
Among the given options,$Sphyrna$ (Hammerhead shark) belongs to the class Chondrichthyes.
$Echeneis$ (Remora),$Hippocampus$ (Sea horse),and $Exocoetus$ (Flying fish) belong to the class Osteichthyes (bony fishes),which do not possess claspers.

(C) $Latimeria$ is known as a living fossil because it has remained morphologically unchanged for several million years,representing a lineage that was thought to be extinct.

(A) The class $Chondrichthyes$ consists of cartilaginous fishes.
These organisms have a cartilaginous endoskeleton.
Examples include sharks,rays,and skates.
In contrast,$Osteichthyes$ refers to bony fishes,and $Agnatha$ refers to jawless fishes.

(B) The $Dipnoans$,commonly known as lungfishes,are a group of sarcopterygian fishes.
Currently,they have a restricted distribution across the Southern Hemisphere.
They are found in the freshwater systems of South America (Latin America),Africa,and Australia.
Among the given options,the combination of Latin America and Australia correctly identifies the regions where these extant species are found.

(C) In fishes,the fins are categorized into paired and unpaired fins.
$1$. Paired fins include the pectoral fins and pelvic fins,which are homologous to the limbs of tetrapods.
$2$. Unpaired fins include the dorsal fin,anal fin,and caudal (tail) fin.
Therefore,the pectoral and pelvic fins are the paired fins.

(A) $Scoliodon$,commonly known as the dogfish,is a member of the class $Chondrichthyes$ (cartilaginous fishes).
Unlike most bony fishes that are oviparous (egg-laying),$Scoliodon$ is viviparous,meaning it gives birth to live young ones.
$Anabas$,$Heteropneustes$,and $Catla$ are all examples of bony fishes $(Osteichthyes)$ that are oviparous.

(A) heterocercal tail is a type of tail fin where the vertebral column extends into the upper lobe,making it larger than the lower lobe.
This type of tail is a characteristic feature of cartilaginous fishes (Class $Chondrichthyes$),such as sharks and rays.
It acts as a steering organ and provides lift during locomotion.

(C) The heart of a fish is known as a $venous$ heart because it only receives and pumps deoxygenated (venous) blood to the gills for oxygenation.
In contrast,other vertebrates like amphibians,reptiles,birds,and mammals have hearts that handle both oxygenated and deoxygenated blood (or separate them completely).
Therefore,the fish heart is unique among vertebrates for exclusively pumping venous blood.

(C) Fishes possess a highly developed lateral line system that is extremely sensitive to vibrations and pressure changes in water.
They also have well-developed eyes for light perception and olfactory organs for detecting chemical cues (odours).
However,their ability to perceive airborne sounds is very limited compared to terrestrial vertebrates,as they lack an external ear and a middle ear structure,making their sense of hearing (sound perception) relatively poor.

(D) The correct answer is $D$.
In $Scoliodon$ (dogfish),a faint lateral line runs along either lateral side of the trunk and tail and over the head region.
This structure marks the position of an underlying sensory lateral line canal system,which opens to the outside at intervals through minute pores.
These organs are characteristic of aquatic vertebrates like fish,which help in detecting vibrations and water currents.

(B) The heart of a fish is described as a $2$-chambered heart,consisting of one atrium and one ventricle.
It is also known as a venous heart because it only pumps deoxygenated blood to the gills for oxygenation.
Therefore,both options $B$ and $C$ are technically correct descriptions of a fish heart. However,in the context of standard biological classification,it is primarily defined as a $2$-chambered venous heart. Given the options provided,if a single choice must be made,$B$ and $C$ are both accurate,but often 'Venous heart' is the specific physiological term used.

(C, D) In fish,fins are classified into paired and unpaired fins.
$1$. Unpaired fins include the dorsal fin,caudal fin (tail fin),and anal fin.
$2$. Paired fins include the pectoral fins and pelvic fins.
Since both $C$ (Pelvic fin) and $D$ (Pectoral fin) are paired,this question typically refers to identifying paired appendages. However,in standard multiple-choice formats where only one answer is expected,both are correct. Given the options,$C$ and $D$ are both paired. Usually,pectoral fins are the primary paired fins.

(C) The $Lateral$ $line$ $system$ is a unique sensory organ found in fishes and some aquatic amphibians.
It consists of a series of fluid-filled canals located along the sides of the body.
These organs contain specialized sensory cells called neuromasts,which detect vibrations,pressure changes,and water currents in the surrounding environment.
This system helps fish in navigation,schooling behavior,and predator avoidance.

(D) In cartilaginous fishes like sharks and rays (Class $Chondrichthyes$),the pelvic fins of the male are modified into specialized structures called $Claspers$.
These $Claspers$ serve as copulatory organs that facilitate the transfer of sperm into the female's cloaca during internal fertilization.
Therefore,the correct option is $D$.

(A) The $Synanceia$ genus,commonly known as the $Stone$ $fish$,is considered the most venomous fish in the world. It possesses sharp spines on its dorsal fin that can inject a potent neurotoxin,which causes extreme pain and can be fatal to humans if not treated immediately.

(D) The fish belonging to the subclass $Dipnoi$ are commonly known as lungfishes.
These fishes possess modified swim bladders that function as lungs,allowing them to breathe atmospheric air.
This adaptation is particularly useful for survival in stagnant or oxygen-poor water bodies.
Therefore,$Dipnoi$ is the correct answer.

(B) $Scoliodon$ belongs to the class $Chondrichthyes$ (cartilaginous fishes).
Members of this class typically exhibit internal fertilization.
In $Scoliodon$,the male possesses pelvic fins modified into claspers,which are used to transfer sperm into the female's cloaca,facilitating internal fertilization.

(D) The $Ampullae$ of $Lorenzini$ are specialized sensory organs found in cartilaginous fishes like $Scoliodon$ (dogfish).
These organs are electroreceptors that are also sensitive to temperature changes,making them thermoreceptors.
They consist of a network of jelly-filled pores that detect weak electrical fields and temperature gradients in the water,aiding the shark in navigation and prey detection.

(A) In fishes,the heart is two-chambered,consisting of one atrium and one ventricle. The heart pumps deoxygenated blood to the gills,where it is oxygenated and then passes directly to the rest of the body. This type of circulation is known as single circulation because the blood passes through the heart only once during each complete cycle of the body. Therefore,fishes exhibit a single-circuit heart.

(B) The heart of a fish is a $2$-chambered heart,consisting of one atrium and one ventricle.
It is known as a venous heart because it only pumps deoxygenated blood to the gills for oxygenation.
Therefore,the heart of a fish receives only deoxygenated blood from the body tissues.

(B) In a closed circulatory system,blood is pumped by the heart through a series of closed vessels (blood vessels).
Among the given options,$A$ (Cockroach),$C$ (Molluscs - except Cephalopods),and $D$ (Scorpion) possess an open circulatory system where blood flows into open spaces called sinuses.
$B$ (Fish) possesses a closed circulatory system where blood remains within vessels throughout the circuit.
Therefore,the correct option is $B$.

(C) Cartilaginous fishes,belonging to the class $Chondrichthyes$,are characterized by a cartilaginous endoskeleton.
These fishes possess $Placoid$ scales on their skin.
$Cycloid$ and $Ctenoid$ scales are typically found in bony fishes (class $Osteichthyes$).
$Ganoid$ scales are found in primitive bony fishes like sturgeons and gars.
Therefore,the correct option is $C$.

(A) The class $Chondrichthyes$ (cartilaginous fishes) exhibits several distinct characteristics:
$1$. Their mouth is located ventrally ($A$ is correct).
$2$. They possess $5$ to $7$ pairs of gills,which are separate and without an operculum ($D$ is also a characteristic,but ventral mouth is a primary diagnostic feature often cited in $NCERT$).
$3$. Their skin is tough,containing minute placoid scales.
$4$. Teeth are modified placoid scales which are backwardly directed.
$5$. Their jaws are very powerful.
$6$. They lack an air bladder,hence they must swim constantly to avoid sinking.
$7$. The caudal fin is heterocercal (not homocercal).
Note: Both $A$ and $D$ are characteristics of $Chondrichthyes$. However,in standard biology examinations,the ventral mouth is the most frequently cited primary characteristic.

(C) The class $Chondrichthyes$ includes cartilaginous fishes,which are characterized by having an endoskeleton composed entirely of cartilage.
Among the given options,$Seahorse$ $(Hippocampus)$,$Labeo$ $(Rohu)$,and $Catla$ $(Catla)$ belong to the class $Osteichthyes$ (bony fishes),which possess a bony endoskeleton.
$Skates$ (members of the order $Rajiformes$) belong to the class $Chondrichthyes$ and possess a cartilaginous endoskeleton.
Therefore,the correct option is $C$.