Phylum - Aschelminthes Questions in English

(A) $Enterobius \ vermicularis$ is not a protozoan. It is a multicellular parasitic nematode (roundworm) belonging to the phylum $Aschelminthes$ (or $Nematoda$),which causes enterobiosis. In contrast,$Paramecium \ caudatum$,$Plasmodium \ vivax$,and $Trypanosoma \ gambiense$ are all unicellular eukaryotic organisms classified as protozoans.

(C) In the $Tube-within-a-Tube$ body plan,the animal's body consists of two tubes: one formed by the body wall and the second formed within it by the digestive tract.
This type of body plan is first observed in the phylum $Aschelminthes$ and continues in all higher phyla up to $Chordata$.
In contrast,$Coelenterates$ and $Platyhelminthes$ exhibit a $Blind-sac$ body plan,where there is only one opening for both ingestion and egestion.

(A) In phylum $Nematoda$ (also known as $Nemathelminthes$ or roundworms),a true coelom is absent.
Instead,they possess a $pseudocoelom$,which is a body cavity that is not lined by mesoderm (peritoneum).
In contrast,phyla such as $Annelida$,$Echinodermata$,and $Mollusca$ possess a true coelom,which is a body cavity derived from the mesoderm and lined by the peritoneum.

(D) The body cavity of an animal is classified based on the presence or absence of a cavity between the body wall and the gut wall.
Animals in which the body cavity is not lined by mesoderm,but instead,the mesoderm is present as scattered pouches in between the ectoderm and endoderm,are called pseudocoelomates.
This condition is a characteristic feature of the phylum $Aschelminthes$ (also known as $Nematoda$).
$Wuchereria$ (filarial worm) and $Ancylostoma$ (hookworm) are members of the phylum $Aschelminthes$.
Therefore,these animals possess a pseudocoelom.

(D) The pseudocoelom is a body cavity that is not lined by mesoderm.
During embryonic development,the blastocoel is the primary cavity formed within the blastula.
In organisms like Aschelminthes (roundworms),the blastocoel persists in the adult stage as the pseudocoelom,as the mesoderm does not line the cavity completely.

(D) $Enterobius$ $vermicularis$ is commonly known as the human 'pin worm' or 'seat worm'. It is considered the most common parasitic nematode infection in humans worldwide.

(A) Pineal setae (also known as spicules) are a characteristic feature of male $Ascaris$.
These structures are situated on the dorsal side of the cloaca.
They play a crucial role during the process of copulation by helping to keep the female genital pore open.

(C) The phylum $Nematoda$ (roundworms) typically exhibits dioecious conditions,meaning the sexes are separate (male and female are distinct).
While some species may show hermaphroditism,it is not a defining or universal characteristic of the phylum as a whole,whereas the other options (elongated cylindrical body,eutely or fixed number of cells,and pseudocoelomate body cavity) are standard diagnostic features of $Nematoda$.
Therefore,the statement 'Hermaphroditism' is the least correct characteristic when describing the general features of the phylum.

(C) The female $Ascaris$ is generally longer,measuring $20-40 \ cm$ in length,whereas the male $Ascaris$ is shorter,measuring $15-30 \ cm$ in length. Additionally,the male has a curved tail with pineal setae,which are absent in the female.

(A) $Ascaris$ is a monogenetic parasite,which means it completes its entire life cycle within a single host. In the case of $Ascaris$ $lumbricoides$,the human being serves as the sole host for its development and reproduction.

(B) In $Ascaris$,the life cycle involves four moultings:
$1$. The $1^{st}$ moulting occurs in the soil.
$2$. The $2^{nd}$ moulting occurs in the intestine of the host.
$3$. The $3^{rd}$ and $4^{th}$ moultings occur in the lungs.
Therefore,the $3^{rd}$ moulting takes place in the lungs.

(A) The $Ascaris$ $lumbricoides$ (roundworm) life cycle involves the development of a $rhabditiform$ larva.
After the ingestion of embryonated eggs,the larvae hatch in the intestine and undergo a complex migration through the circulatory system to the lungs,then back to the intestine to mature into adults.
The first-stage larva that hatches from the egg is known as the $rhabditiform$ larva.

(D) The phylum $Nematoda$ (roundworms) is characterized by a $Pseudocoel$ (false body cavity), a $Non-living$ $cuticle$ covering the body, and a $Syncytial$ $epidermis$ (multinucleate epidermis).
However, it is incorrect to state that all nematodes are parasites in animals. While many species are parasitic in plants and animals, a large number of nematode species are free-living, inhabiting soil, freshwater, and marine environments.
Therefore, the statement '$All$ $are$ $parasites$ $in$ $animals$' is not a typical character of the phylum.

(A) $Ascaris$ possesses specialized sensory organs known as amphids. These structures function as chemoreceptors,which detect chemical stimuli in the environment. They are specifically located on the ventrolateral lips of the organism,aiding in sensory perception.

(A) The infective stage of $Ascaris$ $lumbricoides$ for humans is the embryonated egg.
This egg contains the second-stage juvenile ($L_2$ larva),which is capable of infecting a new host upon ingestion through contaminated food or water.
Once ingested,the eggs hatch in the small intestine,and the larvae penetrate the intestinal wall to begin their migration through the body.

(A) coenocytic condition refers to a multinucleated state where multiple nuclei are present within a single cell or cytoplasm without being separated by cell membranes.
In the phylum $Aschelminthes$ (roundworms),the epidermis of $Ascaris$ is syncytial or coenocytic,meaning it contains many nuclei within a continuous mass of cytoplasm.

(C) $Ascaris$ belongs to the phylum $Aschelminthes$ (or $Nematoda$). In $Ascaris$,the epidermis is syncytial,which means it consists of a multinucleated mass of cytoplasm where individual cell boundaries are absent between adjacent nuclei.

(B) $Ascaris$ is monogenetic,meaning its life cycle is completed in a single host. Its infection occurs through the ingestion of contaminated food and water. In contrast,$Tapeworm$,$Fasciola$,and $Hookworm$ are digenetic,requiring two hosts to complete their life cycle.

(A) Sexual dimorphism refers to the distinct morphological differences between males and females of the same species.
In $Ascaris$ (roundworm),the sexes are separate (dioecious),and the male is smaller than the female with a curved posterior end,exhibiting clear sexual dimorphism.
$Amoeba$ is a unicellular organism that reproduces asexually,so it does not exhibit sexual dimorphism.
$Pheretima$ (earthworm) is hermaphroditic (monoecious),meaning both male and female reproductive organs are present in the same individual,so it does not show sexual dimorphism.
Therefore,the correct answer is $Ascaris$.

(A) The epidermis of $Ascaris$ is syncytial $(coenocytic)$,which means it consists of a multinucleated mass of cytoplasm that is not divided into separate cells by plasma membranes.
This structure is characterized by scattered nuclei within the syncytium and the absence of partition walls between individual nuclei.

(D) Male $Ascaris$ is sexually dimorphic and can be distinguished from the female by its tail end.
The posterior end of the male is curved ventrally and possesses numerous genital papillae.
There are approximately $50$ pairs of pre-anal papillae located in front of the cloaca and $5$ pairs of post-anal papillae located behind it.
Additionally,two chitinous,spicule-like structures of equal size,known as penial setae or spicules,are often seen protruding from the cloacal aperture.
These structures are essential for the transfer of sperm into the female vagina during copulation.
Therefore,all the mentioned features are characteristic of the male $Ascaris$.

(D) In $Ascaris$,sexual dimorphism is observed where the female is longer than the male.
The posterior end of the female $Ascaris$ is straight,whereas the posterior end of the male $Ascaris$ is curved.
Additionally,the male possesses pre-anal and post-anal papillae and penial setae (spicules) for copulation,which are absent in the female.
Therefore,the straight posterior end is a key diagnostic feature to differentiate the female from the male.

(C) $Ascaris$ is a monogenetic parasite, meaning it completes its life cycle in a single host. Therefore, an intermediate host is not required for its development. In contrast, $Liver$ $fluke$, $Tapeworm$, and $Plasmodium$ are digenetic parasites that require at least two hosts to complete their life cycles.

(C) $Ascaris$ lives in the intestine of the host. To survive the harsh environment of digestive enzymes,it employs two primary mechanisms:
$1$. It possesses a thick,resistant $cuticle$ that acts as a physical barrier against enzymatic degradation.
$2$. It secretes $antienzymes$ (or enzyme inhibitors) that neutralize the digestive enzymes of the host.
Therefore,the combination of both $antienzymes$ and $cuticle$ provides effective protection.

(C) $Ascaris$ is a genus of parasitic nematode worms known as the giant intestinal roundworms.
$Ascaris$ exhibits sexual dimorphism,meaning the male and female individuals are separate.
Therefore,$Ascaris$ is unisexual (dioecious),where the male is typically smaller than the female and possesses a curved posterior end.

(C) $Dracunculus$ (Guinea worm) is a digenetic parasite. Its primary host is a human,and its intermediate host is a crustacean known as $Cyclops$ (water flea). When humans drink water contaminated with $Cyclops$ containing the larvae of $Dracunculus$,they become infected.

(D) The life cycle of $Ascaris$ $lumbricoides$ involves migration through various organs of the host.
After ingestion,the eggs hatch in the intestine.
The first moult occurs in the soil or within the egg,but the subsequent larval migrations involve the liver and lungs.
The final (fourth) moult occurs in the intestine,where the larvae mature into adult worms.
Therefore,the site where the larvae complete their development and undergo their final moult is the intestine.

(C) The presence of a resistant,thick cuticle in $Ascaris$ is a specialized adaptation for survival within the host's body.
This cuticle protects the parasite from the host's digestive enzymes and harsh chemical environment.
Therefore,it is a significant characteristic associated with the parasitic mode of life (parasitism).

(C) The life cycle of $Ascaris$ $lumbricoides$ involves the development of the embryo within the egg after it is passed out in the feces.
Inside the egg,the embryo undergoes cleavage and develops into a first-stage larva $(L_1)$,which then molts into a second-stage larva $(L_2)$.
This egg containing the infective second-stage juvenile ($L_2$ larva) is known as the embryonated egg.
Therefore,the correct option is $C$.

(D) The sensory organs in $Ascaris$ are simple elevations supplied by nerves.
These structures include various papillae,amphids,and phasmids.
$1$. Papillae are tactile receptors found around the mouth.
$2$. Amphids are chemoreceptors located on the lateral sides of the head.
$3$. Phasmids are unicellular sensory glands located at the posterior end.
Therefore,all the mentioned structures serve as sensory organs in $Ascaris$.

(A) In $Ascaris$,the excretory system consists of an $H$-shaped canal system.
There is only one excretory pore present in $Ascaris$.
This single excretory pore is situated mid-ventrally,a little behind the mouth region.

(B) The life cycle of $Ascaris$ $lumbricoides$ involves several larval stages.
After the ingestion of embryonated eggs containing the $second$ stage larvae,these larvae hatch in the intestine.
The $second$ stage larva is considered the infective stage for humans.
However,in many biological contexts,the $third$ stage larva is also recognized as a developmental stage that occurs after migration through the lungs and re-entry into the digestive tract.
Therefore,the $second$ and $third$ larval stages are commonly associated with the infective process in the host.

(B) The life span of $Ascaris$ (roundworm) within the human host is typically $9-12$ months. After this period,the adult worms are usually expelled from the body.

(A) $Ascaris$ belongs to the phylum $Aschelminthes$ (roundworms). Its mouth is surrounded by three small,denticulate lips. These lips are arranged as one median dorsal lip and two ventrolateral lips.

(D) The development of $Ascaris$ $lumbricoides$ involves four larval or juvenile stages.
These stages are designated as $L1, L2, L3,$ and $L4$.
The first stage larva $(L1)$ develops within the egg,and the subsequent molting processes occur during the migration of the larvae through the host's body (liver,lungs,and intestine) to reach the adult stage.

(B) $Enterobius$ $vermicularis$,commonly known as the pinworm,causes enterobiasis.
The infection is primarily transmitted through the fecal-oral route,which involves the ingestion of eggs from contaminated surfaces,food,water,or through direct contact with contaminated hands (fomites).
Therefore,the mode of transmission is through contamination.

(D) $Ascaris$ $lumbricoides$ is a human parasite that belongs to the phylum $Aschelminthes$ (roundworms).
Unlike many other parasites, $Ascaris$ $lumbricoides$ has a direct life cycle, meaning it does not require an intermediate host to complete its development.
The parasite infects humans directly through the ingestion of embryonated eggs contaminated with food or water.
Therefore, the correct answer is that there is no intermediate host.

(A) $Ascaris$ $lumbricoides$ exhibits sexual dimorphism.
In this species,the female is generally larger than the male.
The length of the female $Ascaris$ typically ranges from $200$ mm to $350$ mm,whereas the male is smaller,usually ranging from $150$ mm to $250$ mm.
Therefore,the correct size range for the female is $200-350$ mm.

(C) The phenomenon where male and female individuals of a species exhibit distinct external morphological differences is known as sexual dimorphism.
In $Ascaris$ (roundworm),sexual dimorphism is clearly visible.
The male $Ascaris$ is smaller than the female and has a curved posterior end with a pre-anal and post-anal papillae,whereas the female is longer and has a straight posterior end.
$Taenia$ (tapeworm),$Krait$ (snake),and $Sea$ $Anemone$ do not show such distinct external sexual dimorphism in the same manner as $Ascaris$.

(B) The embryonated egg of $Ascaris$ is ingested by the host through contaminated food or water.
Once it reaches the small intestine of the human host,the favorable conditions (temperature and pH) trigger the hatching of the egg.
The second-stage larva (rhabditiform larva) emerges from the egg within the intestine and subsequently begins its migration through the circulatory system to reach the lungs before returning to the intestine to mature.

(C) The infection of $Ancylostoma$ (hookworm) occurs when the infective stage,known as the $Filariform$ larva,comes into contact with human skin.
These larvae are typically found in contaminated soil and penetrate the skin of the host,usually through the feet,to enter the bloodstream and eventually reach the intestine.

(B) The filariform larva is the infective stage of certain parasitic nematodes,which belong to the phylum $Aschelminthes$ (also known as $Nematoda$).
For example,in $Ancylostoma$ $duodenale$ (hookworm),the rhabditiform larva molts into the infective filariform larva,which can penetrate human skin to cause infection.

(C) The body cavity of $Hookworm$ $(Ancylostoma)$ is a pseudocoelom,meaning it is not lined by mesoderm on all sides. Therefore,it is classified as a pseudocoelomate. Leech is a coelomate,Liver fluke is an acoelomate,and Jellyfish is a diploblastic organism without a true coelom.

(B) $Wuchereria$ is an ovoviviparous parasite that releases numerous juveniles known as microfilariae.
Ovoviviparity refers to a reproductive strategy where embryos develop inside eggs that remain within the parent's body until they are ready to hatch.

(C) In animals,the body cavity is a space between the body wall and the gut wall.
If the body cavity is not lined by mesoderm,but instead,the mesoderm is present as scattered pouches in between the ectoderm and endoderm,such a body cavity is called a pseudocoelom.
Phylum $Aschelminthes$ (also known as Nematodes) is the only group among the given options that exhibits this characteristic.
Echinoderms,Molluscs,and Annelids are coelomates,meaning they possess a true coelom lined by mesoderm.

(A) $Ascaris$ $lumbricoides$ is a parasitic nematode that belongs to the phylum $Aschelminthes$.
It is commonly known as the roundworm because its body is circular in cross-section.
$Ancylostoma$ is known as the hookworm,and $Enterobius$ is known as the pinworm or seat worm.

(A) $Ascaris$ (roundworm) belongs to the phylum $Aschelminthes$ (Nematoda).
It exhibits distinct sexual dimorphism,where males and females are separate (unisexual).
The male is smaller than the female and has a curved posterior end.
They possess a pseudocoelom (false body cavity) and their life cycle involves a rhabditiform larva.
Metameric segmentation is a characteristic of $Annelida$,not $Aschelminthes$.
Therefore,sexual dimorphism and the presence of a rhabditiform larva are key differentiating traits.

(B) $Wuchereria$ $bancrofti$ is a filarial nematode that causes filariasis (elephantiasis). The adult worms typically reside in the lymphatic vessels and lymph nodes of the human host. They cause chronic inflammation of the organs in which they live for many years,leading to the characteristic swelling of the lower limbs and other body parts.

(C) The correct option is $C$. The scientific name of the pin worm or seat worm is $Enterobius$ $vermicularis$.
It is a parasitic nematode that commonly inhabits the $caecum$, $colon$, or $vermiform$ $appendix$ of human beings.

(B) In the phylum $Nemathelminthes$ (also known as $Aschelminthes$),the body cavity is not fully lined by the mesoderm (peritoneum).
Instead,the mesoderm is present as scattered pouches between the ectoderm and endoderm.
This type of body cavity is called a $Pseudocoelom$ (false coelom).
Therefore,the correct option is $B$.