Phylum-Mollusca Questions in English

(B) $1$. In option $A$,$Enterobius$ belongs to the phylum Aschelminthes (Nematoda),not Platyhelminthes.
$2$. In option $B$,$Loligo$ (Squid),$Teredo$ (Shipworm),and $Octopus$ (Devil fish) all belong to the phylum Mollusca. This is the correct pairing.
$3$. In option $C$,$Pennatula$ (Sea pen) belongs to the phylum Coelenterata (Cnidaria),not Porifera.
$4$. In option $D$,$Bonellia$ belongs to the phylum Annelida,not Coelenterata.

(B) Ctenidium is a comb-like respiratory organ found in mollusks,particularly gastropods.
During the larval development of gastropods,a process called $Torsion$ occurs,which involves a $180^{\circ}$ rotation of the visceral mass,mantle,and shell.
As a result of this torsion,the ctenidium (along with the anus and mantle cavity) shifts from its original posterior position to an anterior position.
Therefore,the assertion that torsion is seen in the ctenidium is correct.
The reason that the ctenidium acts as a respiratory organ is also a correct biological fact.
However,the process of torsion is a developmental phenomenon and is not caused by the fact that the ctenidium functions as a respiratory organ.
Thus,both statements are correct,but the reason is not the correct explanation for the assertion.

(N/A) $\rightarrow$ Mollusca is the second largest animal phylum.
$\rightarrow$ Molluscs are terrestrial or aquatic (marine or fresh water) and possess an organ-system level of organization.
$\rightarrow$ They are bilaterally symmetrical, triploblastic, and coelomate animals.
$\rightarrow$ The body is covered by a calcareous shell and is unsegmented, with a distinct head, muscular foot, and visceral hump.
$\rightarrow$ The space between the hump and the mantle is called the mantle cavity, in which feather-like gills are present.
$\rightarrow$ These gills perform respiratory and excretory functions.
$\rightarrow$ The anterior head region has sensory tentacles.
$\rightarrow$ The mouth contains a file-like rasping organ for feeding, called the radula.
$\rightarrow$ They are usually dioecious and oviparous, with indirect development.
$\rightarrow$ Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea hare), Dentalium (Tusk shell), and Chaetopleura (Chiton).

(B) Phylum-$Mollusca$ is the second largest phylum of animals.
These organisms are triploblastic,meaning they possess three germ layers (ectoderm,mesoderm,and endoderm).
They are coelomate,meaning they possess a true body cavity lined by mesoderm.
They exhibit an organ-system level of body organization.

(A) The generic name of tusk shell is $Dentalium$. It belongs to the phylum $Mollusca$ and the class $Scaphopoda$. These organisms are characterized by a tubular,tusk-shaped shell that is open at both ends.

(D) The body of animals belonging to phylum-$Arthropoda$ is divided into head,thorax,and abdomen.
In contrast,the body of animals belonging to phylum-$Mollusca$ is unsegmented with a distinct head,a muscular foot,and a visceral hump.

(A) The development in $Mollusca$ can be direct or indirect. In many marine mollusks,the development includes a free-swimming larval stage known as a $trochophore$ larva. Some species also exhibit other larval forms such as the $veliger$ or $glochidium$ (in freshwater mussels). Therefore,the presence of a $trochophore$ larva is a characteristic feature of many mollusks.

(D) The feeding organ in phylum-$Mollusca$ is a $Radula$.
It is a file-like rasping organ used for feeding.
$Ctenedia$ are respiratory organs (gills) in mollusks.
Undulating membranes and suckers are structures found in other groups like protozoans or parasitic worms,not as the primary feeding organ of mollusks.

(B) Phylum-$Mollusca$ lacks $Malpighian$ tubules.
$Malpighian$ tubules are the excretory organs found in phylum-$Arthropoda$ (specifically in insects).
In contrast,mollusks possess feather-like gills located in the mantle cavity,which serve the functions of both respiration and excretion.

(C) The $osphradium$ is a specialized sensory organ found in molluscs,particularly in aquatic gastropods and bivalves.
It functions primarily as a chemoreceptor and mechanoreceptor.
Its main role is to test the physical and chemical properties of the water entering the mantle cavity,which helps in detecting the quality of food and identifying potential predators or environmental changes.
It is typically located at the base of the gills (ctenidia).

(D) The phylum $Mollusca$ is characterized by several key features:
$1$. The body is typically unsegmented.
$2$. The body is often covered by a calcareous shell (made of $CaCO_3$).
$3$. The body is divided into three distinct regions: a head,a muscular foot,and a visceral hump (or visceral mass).
Since all these statements are correct,the correct option is $D$.

(B) In molluscs,the mantle cavity contains feather-like gills (ctenidia). These structures are specialized for gaseous exchange (respiration) and also play a significant role in the process of excretion.

(B) The mouth of molluscs contains a file-like rasping organ with transverse rows of chitinous teeth,which is called the radula.
Radula serves as a feeding or rasping organ in molluscs.

(D) Cephalopod molluscs possess complex,camera-type eyes that are structurally and functionally analogous to the eyes of vertebrates.
This is a classic example of convergent evolution,where unrelated groups evolve similar traits to adapt to similar environmental pressures.

(B) Radula is a file-like rasping organ found in the mouth of molluscs,which bears transverse rows of chitinous teeth.
Radula is primarily used for feeding purposes.

(A) In $Gastropod$ molluscs, the early embryo is symmetrical with an anterior mouth and a posterior anus. However, during development, the visceral mass rotates $180^{\circ}$ relative to the head and foot, bringing the anus near the mouth; this process is known as torsion. As a result, the adult $Gastropod$ becomes asymmetrical.

(D) $Pelecypoda$ (also known as $Bivalvia$) lack a distinct head,tentacles,eyes,jaws,and radula.
Their foot is typically hatchet-shaped and extends between the mantle lobes,used for burrowing into the substrate.
They are primarily filter feeders.
In contrast,the class $Scaphopoda$ possesses prehensile sensory tentacles on the head,and their foot is conical-shaped,adapted for digging.
Therefore,the description provided for $Pelecypoda$ is incorrect.

(D) The Assertion is false because the radula is not present in all molluscs. Specifically,the radula is absent in the class $Pelecypoda$ (also known as $Bivalvia$).
The Reason is also false because the radula is not made of vitrodentine; instead,it is a ribbon-like structure that bears transverse rows of chitinous teeth.
Therefore,both the Assertion and the Reason are incorrect.

(B) Most invertebrates possess an open circulatory system where blood flows into open spaces called sinuses,lacking a capillary network. However,$Cephalopods$ (such as squids and octopuses) possess a closed circulatory system,which includes a well-developed capillary network to facilitate efficient gas exchange and nutrient transport.

(C) connecting link is an organism that exhibits characteristics of two different taxonomic groups,indicating an evolutionary relationship.
$Neopilina$ is a primitive mollusk that shows segmented body structures,which is a characteristic feature of $Annelida$,while also possessing typical molluscan features like a shell and a mantle.
Therefore,$Neopilina$ serves as a connecting link between the phylum $Annelida$ and $Mollusca$.

(B) $\rightarrow$ Location: The mouth of mollusks contains a file-like rasping organ known as the radula.
$\rightarrow$ Function: It acts as a rasping organ that assists in the process of feeding by scraping food particles.

(B) The radula is a file-like,rasping organ present in the buccal cavity of most molluscs.
It functions primarily in feeding by scraping or rasping food particles.
Additionally,it is used for boring or creating depressions in rocks,which these animals often use as a habitat or shelter.

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

(D) Snails belong to the phylum $Mollusca$.
In mollusks,the mantle cavity contains feather-like gills (ctenidia).
These gills serve two primary functions: they are involved in respiration (gas exchange) and also play a role in excretion.
Therefore,both respiration and excretion are the correct functions.

(A) The radula is a file-like rasping organ present in the mouth of mollusks.
It is used for feeding and is a characteristic feature of the phylum $Mollusca$.
Since it is involved in the process of ingestion and food processing,it is considered a part of the digestive system.

(D) The phylum $Mollusca$ is the second-largest animal phylum.
Its body is unsegmented with a distinct head,a muscular foot,and a 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.

(B) The animal shown in the image is an Octopus,which belongs to the phylum Mollusca.
Most mollusks,including cephalopods like the Octopus,exhibit bilateral symmetry,meaning their body can be divided into two identical left and right halves along a single plane.

(A) The phylum $Mollusca$ is characterized by an unsegmented body with a distinct head,a muscular foot,and a visceral hump.
These organisms typically have a mantle cavity and a shell (though not always present).
$Echinodermata$ are characterized by a water vascular system and radial symmetry in adults.
$Hemichordata$ are worm-like marine animals with a proboscis,collar,and trunk.
$Annelida$ are characterized by a segmented body (metamerism).

(A) The radula is a specialized anatomical structure found in the phylum $Mollusca$.
It is a file-like,rasping organ used for feeding,which helps in scraping food particles.
Among the given options,$Sepia$ belongs to the class $Cephalopoda$ of the phylum $Mollusca$.
$Asterias$ belongs to the phylum $Echinodermata$,$Balanoglossus$ belongs to the phylum $Hemichordata$,and $Musca$ belongs to the phylum $Arthropoda$ (class $Insecta$).
Therefore,the correct answer is $Sepia$.

(C) The $Radula$ is a unique anatomical structure found in the phylum $Mollusca$ (except in bivalves).
It is a chitinous,ribbon-like structure equipped with rows of small teeth,which functions as a file-like rasping organ used for scraping or cutting food particles.
Therefore,the correct answer is $Mollusca$.

(C) The body of mollusks is unsegmented with a distinct head,muscular foot,and visceral hump. Among the given options,the $Snail$ belongs to the Phylum $Mollusca$. $Starfish$ belongs to $Echinodermata$,$Balanoglossus$ belongs to $Hemichordata$,and $Locust$ belongs to $Arthropoda$. Therefore,the correct answer is $Snail$.