Phylum-Mollusca Questions in English

(D) The term 'Cephalopoda' is derived from the Greek words 'kephale' meaning 'head' and 'podos' meaning 'foot'.
In these mollusks,the foot is modified into tentacles or arms that are directly attached to the head region.
Therefore,the characteristic feature is that the appendages (tentacles/arms) are located on the head.

(C) Pearls are produced by certain members of the phylum $Mollusca$,specifically within the class $Bivalvia$ (e.g.,pearl oysters like $Pinctada$).
When a foreign particle,such as a grain of sand or a parasite,enters the mantle cavity of the oyster,the mantle tissue secretes layers of calcium carbonate $(CaCO_3)$ around the irritant to protect itself.
Over time,these layers form a pearl.

(C) The $Osphradium$ is a sensory organ found in many mollusks,including $Pila$ (apple snail). It functions as a chemoreceptor,which is used to test the chemical nature of the water entering the mantle cavity. Therefore,the correct option is $C$.

(D) Sepia belongs to the phylum $Mollusca$ and the class $Cephalopoda$.
It is commonly referred to as the $Cuttlefish$.
Starfish belongs to the phylum $Echinodermata$.
Jellyfish belongs to the phylum $Cnidaria$.
Therefore,the correct option is $D$.

(C) Keber's organ,also known as the pericardial gland,is a specialized excretory organ found in mollusks,particularly in bivalves like Unio.
It is associated with the pericardium and functions in the excretion of nitrogenous waste products.
Therefore,it is an associated part of the pericardium.

(B) The organism commonly known as the Apple snail is $Pila$.
$Pila$ belongs to the phylum $Mollusca$ and the class $Gastropoda$.
It is a freshwater mollusk characterized by a spirally coiled shell.
$Turbinella$ is known as the Shankha,$Cypraea$ is known as the Cowrie,and $Aplysia$ is known as the Sea hare.

(D) Muller's ciliated organ is a specialized structure found in the larvae of certain mollusks,particularly in the class $Bivalvia$ (e.g.,$Unio$). It is a ciliated organ that helps in the movement and sensory perception of the larva. It is not an osphradium,velum,or gill pouch. Therefore,the correct answer is $D$ (None of the above).

(C) The animal kingdom is classified into various phyla based on their body organization and characteristics.
$1$. Arthropoda is the largest phylum of the animal kingdom,comprising about two-thirds of all named species on Earth.
$2$. Mollusca is the second largest phylum of the animal kingdom.
$3$. Therefore,the correct answer is Mollusca.

(A) $Pila$ (commonly known as the apple snail) belongs to the phylum $Mollusca$.
Within the phylum $Mollusca$,$Pila$ is classified under the class $Gastropoda$.
$Gastropoda$ is the largest class in the phylum $Mollusca$,characterized by a distinct head,a muscular foot,and a spirally coiled shell.

(D) The phylum $Mollusca$ includes diverse organisms. Among these,the class $Cephalopoda$ (which includes squids,octopuses,and cuttlefish) is considered the most active and intelligent group. They possess a well-developed nervous system,complex eyes,and a highly efficient circulatory system,which allows them to be active predators in marine environments. Therefore,the correct answer is $D$.

(C) The ink gland (or ink sac) is a specialized organ found in many cephalopods,including $Sepia$ (cuttlefish).
It is used as a defense mechanism to release a cloud of dark ink into the water,which helps the animal escape from predators by obscuring their vision.

(A) The phylum $Mollusca$ is characterized by the presence of a file-like rasping organ for feeding,which is known as the $Radula$. This organ is located in the buccal cavity and helps in scraping food particles.

(C) In certain mollusks,particularly in terrestrial gastropods like snails,the eyes are situated at the tips of a pair of retractable,stalk-like structures known as $Ommatophores$ (or eye stalks). These structures allow the animal to extend its eyes to sense the environment while keeping the rest of its body protected.

(A) In the phylum Mollusca, respiration typically occurs through specialized gills known as $Ctenidia$.
These are feather-like structures located in the mantle cavity that facilitate gaseous exchange in aquatic mollusks.
$Trachea$ are respiratory tubes found in insects.
$Book \text{ } lungs$ are respiratory organs found in arachnids.
$Keber's \text{ } organ$ is an excretory structure (pericardial gland) found in bivalve mollusks, not a respiratory organ.

(A) In most mollusks,the circulatory system is open,meaning blood flows through sinuses or open spaces called hemocoel.
However,the class $Cephalopoda$ (which includes squids,octopuses,and cuttlefish) is an exception.
These organisms possess a closed circulatory system where blood is confined within blood vessels,which allows for more efficient oxygen transport to support their active,predatory lifestyle.

(B) In the phylum $Mollusca$,specifically in the class $Cephalopoda$ (which includes $Octopus$,$Sepia$,and $Loligo$),the foot is modified into a set of arms or tentacles located around the head region. Therefore,these arms are considered modified foot structures.

(C) The study of molluscan shells is known as Conchology.
Malacology is the study of mollusks as a whole (including their anatomy,physiology,and ecology).
Mammalogy is the study of mammals.
Shellology is a less formal term often used interchangeably with Conchology,but Conchology is the scientifically recognized term for the study of shells.

(A) The $Osphradium$ is a sensory organ found in certain mollusks,such as aquatic gastropods and bivalves. Its primary function is to test the chemical properties of the water entering the mantle cavity. Therefore,it acts as a chemoreceptor,helping the organism detect food or potential threats in the surrounding water.

(A) The organism $Neopilina$ is considered a living fossil and serves as a connecting link between the phyla $Annelida$ and $Mollusca$. It exhibits characteristics of both groups,such as the presence of repeated gills and nephridia (typical of $Annelida$) along with a shell and a mantle (typical of $Mollusca$).

(C) The phylum $Mollusca$ exhibits significant diversity in its circulatory systems.
While most mollusks (such as snails and bivalves) possess an open circulatory system,the class $Cephalopoda$ (which includes squids,octopuses,and cuttlefish) possesses a closed circulatory system.
Therefore,this phylum contains animals with both types of circulatory systems.

(A) The phylum $Mollusca$ is characterized by soft-bodied animals.
$Dentalium$,commonly known as the tusk shell,belongs to the phylum $Mollusca$.
$Peripatus$ belongs to the phylum $Arthropoda$.
$Waucheria$ (Wuchereria) is a nematode belonging to the phylum $Aschelminthes$.
$Planaria$ is a flatworm belonging to the phylum $Platyhelminthes$.
Therefore,the correct option is $A$.

(C) The body of mollusks is covered by a calcareous shell.
This shell is primarily composed of $CaCO_3$ (calcium carbonate) in the form of calcite or aragonite crystals embedded in a protein matrix.
Therefore,the correct structural component of the shell in phylum Mollusca is calcium carbonate.

(C) In molluscs,the body is covered by a calcareous shell and is unsegmented with a distinct head,muscular foot,and visceral hump. $A$ soft and spongy layer of skin forms a mantle over the visceral hump. The space between the hump and the mantle is called the mantle cavity,in which feather-like gills are present. Therefore,the mantle cavity is located between the visceral hump (body wall) and the mantle.

(B) In the phylum $Mollusca$, the body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot, and visceral hump. A soft and spongy layer of skin forms a mantle over the visceral hump. The space between the visceral hump and the mantle is called the $mantle \text{ } cavity$. In this cavity, feather-like gills are present which have respiratory and excretory functions. Therefore, the correct answer is the mantle cavity.

(B) The phylum $Mollusca$ exhibits a wide range of reproductive and developmental characteristics.
$1$. Most mollusks are dioecious (unisexual),but some are hermaphroditic.
$2$. Fertilization can be external (as in many bivalves) or internal (as in cephalopods and gastropods).
$3$. Development is usually indirect (involving a larval stage like trochophore or veliger),but it can be direct in some species (like cephalopods).
Therefore,the correct option is $B$.

(C) The Phylum $Mollusca$ includes soft-bodied animals.
$Chiton$ (Chiton),$Dentalium$ (Tusk shell),$Sepia$ (Cuttlefish),and $Octopus$ (Devil fish) are all members of the Phylum $Mollusca$.
Option $A$ is incorrect because Prawn and Cockroach belong to Phylum $Arthropoda$.
Option $B$ is incorrect because Nereis belongs to Phylum $Annelida$ and Peripatus is an $Arthropod$.
Option $D$ is incorrect because Planaria and Tapeworm belong to Phylum $Platyhelminthes$,Ascaris belongs to $Aschelminthes$,and Earthworm belongs to $Annelida$.

(D) The structure present in the mouth of mollusks (specifically in the class Gastropoda,Cephalopoda,etc.) that is used for feeding is called the $Radula$. The $Radula$ is a rasping,tongue-like organ equipped with transverse rows of chitinous teeth. It is supported by a cartilaginous structure known as the $Odontophore$. The $Radula$ is located within the $Buccal$ $cavity$. Since all these components are associated with the feeding apparatus in the mouth of these animals,the correct answer is $D$.

(B) The radula is a specialized rasping,tongue-like organ found in the mouth of most mollusks (except bivalves). It is equipped with rows of chitinous teeth used for scraping or grinding food particles before they enter the digestive tract. Therefore,its primary function is the grinding or rasping of food.

(B) The features mentioned—a shell of calcium carbonate,a mantle (a soft fleshy layer),and a radula (a file-like rasping organ for feeding)—are the diagnostic characteristics of the phylum $Mollusca$.
$Pila$ (Apple snail) belongs to the phylum $Mollusca$,class $Gastropoda$,and exhibits all these features.
$Prawn$ belongs to the phylum $Arthropoda$.
$Turtle$ belongs to the phylum $Chordata$ (class $Reptilia$).
$Sandworm$ belongs to the phylum $Annelida$.

(B) The animal $Chiton$ belongs to the phylum $Mollusca$.
Members of the phylum $Mollusca$ typically possess a hard,calcareous shell (exoskeleton) made of calcium carbonate $(CaCO_3)$ that provides protection to their soft bodies.
$Jellyfish$ belongs to $Cnidaria$ and lacks such a shell.
$Leech$ belongs to $Annelida$ and has a soft,segmented body without an exoskeleton.
$Ascidia$ belongs to $Urochordata$ (Chordata) and possesses a tunic made of tunicin,not a calcium carbonate exoskeleton.

(B) Most molluscs have an open circulatory system. In these animals,the respiratory pigment is $Hemocyanin$,which contains copper. Unlike hemoglobin,which is found in red blood cells in vertebrates,$Hemocyanin$ is dissolved directly in the blood plasma. This gives the blood a blue color when oxygenated.

(A) In $Dentalium$,which belongs to the phylum $Mollusca$ (class $Scaphopoda$),the excretory organs are a pair of kidneys. These are also known as $Bojanus$ organs or nephridia,which function to filter nitrogenous waste from the hemolymph and excrete it into the mantle cavity. Therefore,the correct answer is $A$.

(D) In $Pila$ (a member of the phylum $Mollusca$),the mouth contains a rasping,file-like organ used for feeding called the $Radula$. This structure is characteristic of most mollusks and is used to scrape food particles.

(A) In the phylum $Mollusca$,the space between the visceral hump and the mantle is called the mantle cavity.
This cavity contains feather-like gills,which are known as $Ctenidia$.
These gills have respiratory and excretory functions.

(A) Mollusks possess a file-like rasping organ for feeding,which is called the $Radula$. This structure is equipped with transverse rows of chitinous teeth,which help in scraping or grinding food particles.

(B) In mollusks,the body is covered by a calcareous shell and is unsegmented with a distinct head,muscular foot,and visceral hump. $A$ soft and spongy layer of skin forms a mantle over the visceral hump. The space between the visceral hump and the mantle is called the mantle cavity. In this mantle cavity,feather-like gills are present,which have respiratory and excretory functions.

(A) $1$. $Chiton$ belongs to the phylum $Mollusca$. Animals in this phylum exhibit organ-system level of organization and are typically unsegmented.
$2$. $Scorpion$ $(Arthropoda)$ is segmented.
$3$. $Peripatus$ $(Onychophora)$ is segmented.
$4$. $Crab$ $(Arthropoda)$ is segmented.
Therefore,$Chiton$ is the correct answer as it is an unsegmented animal with organ-system level of organization.

(D) The body of mollusks is covered by a calcareous shell. This shell is primarily composed of calcium carbonate $(CaCO_3)$. It provides protection to the soft body of the animal.

(D) $Dentalium$ is a genus of marine scaphopod mollusks,commonly known as 'tusk shells' or 'tooth shells'.
They belong to the phylum $Mollusca$.
These animals are characterized by their tubular,conical shells that are open at both ends.

(C) In the phylum $Mollusca$,the body is covered by a calcareous shell and is unsegmented with a distinct head,muscular foot,and visceral hump. $A$ soft and spongy layer of skin forms a mantle over the visceral hump. The space between the hump and the mantle is called the $mantle$ $cavity$,in which feather-like gills are present. These gills have respiratory and excretory functions.

(B) The phylum $Mollusca$ exhibits a wide range of body symmetries. While most mollusks are bilaterally symmetrical,some,like certain gastropods (e.g.,snails),exhibit asymmetry due to torsion during development. Additionally,some primitive forms or specific structures within the phylum can show radial-like arrangements. Therefore,$Mollusca$ is the correct answer as it encompasses representatives showing asymmetry,radial symmetry,and bilateral symmetry across its diverse classes.

(B) In mollusks,the mantle is a soft,fleshy fold of the body wall that secretes the shell. The space between the body wall (visceral mass) and the mantle is known as the mantle cavity. This cavity contains the gills (ctenidia),which are involved in respiration and excretion.

(D) : Mollusca includes those animals which have soft bodies,usually furnished with a shell. The body is often divided into a head,with eyes or tentacles,a muscular foot,and a visceral mass housing the organs. $Loligo$ (squid or sea arrow),$Teredo$ (shipworm),and $Octopus$ are some of their examples.
In option $A$,$Spongilla$ and $Euplectella$ belong to Porifera,but $Pennatula$ (the sea pen or sea feather) belongs to Coelenterata (Cnidaria).
In option $B$,$Physalia$ and $Aurelia$ belong to Cnidaria,but $Bonellia$ belongs to Phylum Annelida.
In option $C$,$Planaria$ and $Schistosoma$ belong to Platyhelminthes,but $Enterobius$ (pinworm) belongs to Aschelminthes.

(C) In an open circulatory system,the blood is pumped out of the heart into blood spaces or sinuses called haemocoel.
This type of circulatory system is characteristic of arthropods and most molluscs (except cephalopods).
Fishes,amphibians,and annelids (like earthworms) possess a closed circulatory system where blood flows through a network of closed vessels.

(A) The radula is a rasping,tongue-like organ found in the mouth of most mollusks.
It is used for feeding,functioning like a file to scrape or cut food before it enters the esophagus.
This structure is a characteristic feature of the phylum $Mollusca$ (except for bivalves).
Therefore,the correct option is $A$.

(A) The mantle cavity is a characteristic feature of the phylum $Mollusca$.
It is the space between the visceral mass and the mantle (a fleshy fold of skin).
$Sepia$ (cuttlefish) belongs to the class $Cephalopoda$ of the phylum $Mollusca$ and possesses a mantle cavity.
$Balanoglossus$ belongs to $Hemichordata$,$Ophiyura$ (brittle star) belongs to $Echinodermata$,and $Fasciola$ (liver fluke) belongs to $Platyhelminthes$.
Therefore,the correct option is $A$.

(B) The animal kingdom is classified into various phyla based on their body organization and characteristics.
$1$. Arthropoda is the largest phylum in the animal kingdom,comprising approximately two-thirds of all named species on Earth.
$2$. Mollusca is the second largest phylum in the animal kingdom,characterized by a soft body,a mantle,and often a calcareous shell.
Therefore,the correct answer is $B$ (Mollusca).

(B) $Teredo$,commonly known as the shipworm,is a genus of saltwater clams in the family $Teredinidae$.
These molluscs are famous for boring into submerged wood,such as ship hulls and piers,which is why they are referred to as wood-boring molluscs or shipworms.
$Chiton$ is a marine mollusc known as the coat-of-mail shell.
$Limax$ is a genus of slugs.
$Patella$ is a genus of sea limpets.

(D) The members of the class $Cephalopoda$ (e.g.,octopus,squid) possess complex,camera-type eyes that are remarkably similar in structure and function to the vertebrate eye. Both types of eyes feature a lens,iris,and retina,representing a classic example of convergent evolution.

(C) In a closed circulatory system,blood is pumped through vessels of varying diameters (arteries,veins,and capillaries).
Among the given options:
$1$. Snails (Mollusca) typically have an open circulatory system.
$2$. Cockroaches (Arthropoda) have an open circulatory system.
$3$. Cuttlefish (Cephalopoda,Mollusca) possess a closed circulatory system,which is an exception within the phylum Mollusca.
Therefore,the correct answer is $C$.