Phylum-Coelenterata (Cnideria) Questions in English

(B) $Hydra$ possesses a very primitive nervous system consisting of a nerve net of bipolar and multipolar nerve cells.
Unlike higher animals,it lacks a centralized nervous system or a brain.
Therefore,$Hydra$ has a nervous system but no brain.

(A) $Hydra$ possesses four distinct types of nematocysts,which are specialized stinging cells used for prey capture and defense.
$1$. Penetrants (Stenoteles): These are the largest nematocysts and contain a barbed thread that injects toxins into the prey.
$2$. Volvents (Desmonemes): These are the smallest nematocysts; they possess a short,thick,spineless thread that coils around the prey's appendages.
$3$. Steroline Glutinants (Atrichous isorhizas): These are small,oval-shaped nematocysts that secrete a sticky substance to adhere to the prey.
$4$. Streptoline Glutinants (Holotrichous isorhizas): These are larger,elongated nematocysts that also secrete adhesive substances.
Therefore,penetrant,volvent,and glutinant are all types of nematocysts found in $Hydra$.

(C) The mesogloea is a viscous,transparent,and jelly-like mucopolysaccharide substance secreted by the cells of both epithelia.
It contains a regular network of long collagen or elastin fibres,but it does not contain any cells.

(D) The gastrovascular cavity,also known as the coelenteron,is a central digestive compartment in $Hydra$.
It performs two primary functions: digestion of food and the circulation of nutrients throughout the body.
Since $Hydra$ lacks a specialized circulatory system,the gastrovascular cavity facilitates the distribution of digested food to all cells.

(B) In $Hydra$,the testes are temporary structures that develop in the body wall.
They are typically located in the distal half of the body,specifically near the base of the tentacles.
This positioning facilitates the release of sperm into the surrounding water for fertilization.

(A) Zoochlorellae and zooxanthellae are unicellular algae that live as symbionts within the nutritive-muscular cells of $Hydra$.
These algae provide oxygen and carbohydrates to the $Hydra$ through photosynthesis,while the $Hydra$ provides protection and nitrogenous waste to the algae.

(D) $Hydra$ belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
These organisms possess a central gastro-vascular cavity with a single opening,the mouth on the hypostome.
This cavity is known as the $Coelenteron$ or the $Gastrovascular$ $cavity$.
Therefore,both terms refer to the same structure in $Hydra$.

(C) $Corallium$ is commonly known as the precious red coral.
It belongs to the class $Anthozoa$ of the phylum $Cnidaria$.
Due to its hard,durable skeleton and vibrant red color,it is highly valued and widely used in the manufacturing of jewelry and ornaments.

(D) The correct answer is $D$. $A$ sexually mature medusa of $Obelia$ bears four groups of gonads. These gonads are situated on the middle of the four radial canals on the oral surface of the medusa.

(C) In $Hydra$,digestion is both extracellular and intracellular.
The gastrodermis contains gland cells that secrete digestive enzymes into the gastrovascular cavity for extracellular digestion.
These enzymes primarily act on proteins and fats.
Intracellular digestion occurs within the food vacuoles of the nutritive-muscular cells,where further breakdown of nutrients,including some carbohydrates,takes place.
Therefore,the gastrodermis is involved in the digestion of proteins,fats,and some carbohydrates.

(B) The body wall of $Hydra$ consists of two layers: the outer epidermis and the inner gastrodermis.
Stinging cells,also known as $cnidocytes$ or $nematocysts$,are specialized cells used for defense and capturing prey.
These $cnidocytes$ are exclusively found in the epidermis (ectoderm) of $Hydra$.
Therefore,they are absent in the gastrodermis.

(D) $Hydra$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
In $Hydra$,the muscle fibers are known as epitheliomuscular cells.
These cells are specialized cells of the epidermis that contain contractile myofibrils at their base.
These are neither true smooth muscles nor skeletal muscles as found in higher vertebrates.
Therefore,the correct answer is that none of the given options describe the muscles of $Hydra$ accurately.

(A) $Hydra$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
In $Hydra$,the nervous system consists of a network of nerve cells (neurons) distributed throughout the body,but these cells are not organized into distinct nerves or a central nervous system.
This is known as a diffuse or nerve net type of nervous system.
In contrast,organisms like $Tapeworms$,$Earthworms$,and $Frog's$ $tadpoles$ possess more complex nervous systems that include organized nerves and ganglia.

(D) Nematocysts are specialized stinging cells found in the phylum $Cnidaria$.
They contain a coiled thread that can be rapidly everted to inject toxins.
These structures are essential for $3$ primary functions:
$1$. $Food \text{ } capture$: They paralyze prey to facilitate feeding.
$2$. $Offence$: Used to attack other organisms.
$3$. $Defence$: Used to protect the organism from predators.
In some species, they also assist in $locomotion$ by anchoring the organism to a substrate.
Therefore, all the given options are correct.

(D) The sea fan,scientifically known as $Gorgonia$,belongs to the phylum $Coelenterata$ (also known as $Cnidaria$).
These organisms are aquatic,mostly marine,sessile or free-swimming,and radially symmetrical animals.
They are characterized by the presence of cnidoblasts or cnidocytes on the tentacles and the body,which are used for anchorage,defense,and the capture of prey.

(B) Nematocysts are specialized stinging organelles found in the cells called cnidocytes,which are characteristic of the phylum $Cnidaria$.
These organelles are activated by mechanical stimulation of the cnidocil (a sensory hair-like structure).
When an object touches the cnidocil,it triggers a rapid change in the permeability of the nematocyst membrane,leading to the discharge of the thread-like tubule.
Therefore,touch is the primary stimulus for the activation of nematocysts.

(C) $Physalia$ is commonly known as the 'Portuguese Man of War'.
It is named so because of its resemblance to an $18^{th}$-century Portuguese warship at full sail.
It is a pelagic,marine,colonial hydrozoan belonging to the phylum $Cnidaria$ (or $Coelenterata$).

(A) The body wall of $Hydra$ consists of two layers: the outer epidermis and the inner gastrodermis (endoderm).
$1$. Stinging cells (cnidoblasts) are specialized cells used for defense,offense,and anchorage,which are exclusively found in the epidermis.
$2$. Interstitial cells are undifferentiated,totipotent cells found in the epidermis that can transform into any other cell type.
$3$. Gland cells are primarily found in the gastrodermis (endoderm) to secrete digestive enzymes.
Therefore,stinging cells and interstitial cells are characteristic of the epidermis and are absent in the endoderm.

(A) In $Hydra$,the interstitial cells are undifferentiated,totipotent cells. During the reproductive phase,these interstitial cells become active and undergo repeated multiplication to form germ cells. These germ cells aggregate and bulge out from the body wall to form gonads (testes or ovaries).

(B) $Hydra$ is a carnivorous organism belonging to the phylum $Cnidaria$. It primarily feeds on small aquatic animals such as $Daphnia$,$Cyclops$,and other small crustaceans or insect larvae. It captures its prey using tentacles equipped with stinging cells called $cnidocytes$ (or $nematocysts$).

(B) The $Mesoglea$ in $Hydra$ is an undifferentiated,gelatinous,non-cellular layer located between the outer epidermis and the inner gastrodermis.
It is primarily composed of a thin,jelly-like matrix containing proteins and mucopolysaccharides,but it lacks any cellular components or fibers.
Among the given options,it is essentially a proteinaceous matrix.

(D) The phylum $Coelenterata$ (also known as $Cnidaria$) is characterized by the presence of a central gastrovascular cavity with a single opening called the $hypostome$ (mouth),which serves both for ingestion and egestion.
While tentacles are present in many cnidarians,the gastrovascular cavity is a more fundamental and defining anatomical feature of the phylum.
Therefore,the presence of a gastrovascular cavity is the most characteristic feature among the given options.

(A) $Fungia$ is a genus of corals in the family $Fungiidae$.
It is commonly known as the Mushroom Coral because of its solitary,disc-like shape that resembles the cap of a mushroom.
Therefore,the correct option is $A$.

(D) In $Hydra$,nematocysts are specialized structures found within cells called cnidoblasts (or cnidocytes). These cnidoblasts are derived from undifferentiated,pluripotent cells known as interstitial cells located in the epidermis. As the interstitial cells divide and differentiate,they give rise to new cnidoblasts,which then produce nematocysts.

(A) The medusa of $Obelia$ is strictly carnivorous in its feeding habit.
It captures prey using its tentacles and nematocysts.
Its diet primarily consists of minute worms,nematodes,small insects,and crustaceans.

(B) The sense organs of $Aurelia$ (a member of the phylum $Cnidaria$,class $Scyphozoa$) are called $rhopalia$ or $tentaculocysts$.
These structures are marginal sense organs that contain statocysts for equilibrium and sometimes ocelli for light sensitivity.
$Tentilla$ are small tentacles,$nematocysts$ are stinging cells,and $otoliths$ are the calcified structures found within the statocysts.

(D) In $Hydra$,the germ cells (gametes) are not derived from a specific germ layer like the ectoderm or endoderm.
Instead,they originate from undifferentiated,pluripotent cells known as $Interstitial$ $cells$ (or $I-cells$).
These $Interstitial$ $cells$ are located in the ectoderm and can differentiate into various cell types,including gametes,during the reproductive phase.

(C) $Hydra$ is a polyp-like or polypoid coelenterate with a tubular or cylindrical body.
It belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
$Cnidarians$ exhibit two basic body forms: the $polyp$ and the $medusa$.
The $polyp$ form is sessile and cylindrical,like $Hydra$ and $Adamsia$,whereas the $medusa$ form is umbrella-shaped and free-swimming,like $Aurelia$.

(A) The ectoderm (epidermis) of $Hydra$ is composed of several types of cells.
The most abundant cells in the epidermis are the musculo-epithelial cells (also known as epithelio-muscular cells).
These cells cover the entire outer surface of the body and possess contractile basal processes that help in the movement of the organism.
Therefore,the correct option is $A$.

(C) In this method of locomotion of $Hydra$,the body usually first extends and then bends over,so that the tentacles attach to the substratum with the help of adhesive $atrichous$ $isorhizas$ (also known as $glutinants$).

(D) Thigmotaxis is the movement or orientation of an organism in response to a touch or physical contact stimulus.
$Hydra$ exhibits thigmotaxis,which allows it to respond to contact with surfaces or prey by adjusting its position or triggering its tentacles.
$Ascaris$ and $Taenia$ are parasitic worms that do not primarily exhibit this behavior in the same manner as $Hydra$.
$Fungia$ is a coral that is generally sessile and does not exhibit active thigmotactic movement.

(C) Nematocysts are specialized stinging cells found in the tentacles of $Hydra$.
When a prey item comes into contact with the tentacles,the nematocyst is triggered to discharge.
Upon stimulation,the operculum opens,and the thread-tube is everted,which pierces the prey and injects toxins to paralyze it.
Therefore,the ejection is a response to physical or chemical contact,not a conditioned reflex,and they are not re-used after discharge.

(B) $Hydra$ possesses a high power of regeneration. For a fragment to successfully regenerate into a complete organism,it must contain both the outer layer $(Epidermis)$ and the inner layer $(Gastrodermis)$. These layers contain interstitial cells,which are undifferentiated cells capable of dividing and differentiating into various cell types required to form a new $Hydra$.

(D) Bilateral symmetry is a body plan where the organism can be divided into two identical left and right halves along a single plane.
$1$. $Frog$ (Amphibia), $Octopus$ (Mollusca), and $Mammal$ (Mammalia) all exhibit bilateral symmetry in their adult forms.
$2$. $Obelia$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
$3$. Members of the phylum $Cnidaria$ typically exhibit radial symmetry, not bilateral symmetry.
Therefore, the correct answer is $Obelia$.

(B) $Ctenophores$ share certain morphological and physiological characteristics with the members of the phylum $Coelenterata$ (also known as $Cnidaria$),such as radial symmetry,diploblastic organization,and the presence of a gastrovascular cavity. However,there is no evolutionary evidence to suggest that $Ctenophores$ were directly derived from $Coelenterates$.

(A) The life cycle of $Hydra$ does not typically include a free-swimming larval stage like many other Cnidarians. However,in some contexts,the term $Hydrula$ is used to describe the small,simple,polyp-like stage that develops directly from the embryo. $Hydratuba$ and $Scyphula$ are larval stages associated with the class $Scyphozoa$ (e.g.,$Aurelia$),and $Planula$ is the common ciliated larva found in many Cnidarians. Therefore,$Hydrula$ is the stage associated with $Hydra$ development.

(B) Hydra is a predatory organism that captures its prey using specialized cells called cnidocytes,which contain nematocysts.
However,the initial recognition of the prey is triggered by chemical stimuli.
When the prey comes in contact with the tentacles of the $Hydra$,the chemical substances released by the prey are detected by the sensory cells on the tentacles,which then trigger the discharge of the nematocysts to capture the prey.

(C) $Choanocytes$ (collar cells) are specialized flagellated cells that line the inner chambers of sponges ($Phylum$ $Porifera$). They are not found in $Hydra$, which belongs to $Phylum$ $Cnidaria$. $Hydra$ contains epithelio-muscular cells, cnidocytes (stinging cells), and nerve cells as part of its body organization.

(A) Sea-anemone belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
Adult sea-anemones exhibit $Radial$ symmetry, where the body can be divided into identical halves by any plane passing through the central axis.
While some cnidarians show variations, the characteristic symmetry for adult sea-anemones is $Radial$ symmetry.

(C) The sea anemone,scientifically known as $Adamsia$,belongs to the phylum $Coelenterata$ (also known as $Cnidaria$).
These organisms are characterized by the presence of $cnidoblasts$ or $cnidocytes$ on the tentacles and body,which are used for anchorage,defense,and capturing prey.
They exhibit radial symmetry and are diploblastic animals.

(A) Animals in the phylum $Cnidaria$ (such as jellyfish,sea anemones,and corals) exhibit radial symmetry.
This means that their body parts are arranged around a central axis,and any plane passing through this central axis divides the body into two identical halves.

(C) $Hydra$ belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
$Cnidarians$ are characterized by being $diploblastic$,meaning they have two germ layers: an outer $ectoderm$ and an inner $endoderm$.
They exhibit $radial$ $symmetry$ in their body plan.
They lack a true body cavity,making them $acoelomate$ organisms.
Therefore,the correct description for $Hydra$ is $diploblastic$,$radial$ $symmetry$,and $acoelomate$.

(B) Diploblastic animals are those in which the cells are arranged in two embryonic layers,an external ectoderm and an internal endoderm.
Cnidarians,such as Sea Anemone,are characteristically diploblastic.
They are also acoelomate,meaning they lack a true body cavity (coelom).
$Ascaris$ is a pseudocoelomate (nematode).
$Planaria$ is a triploblastic,acoelomate flatworm.
$Periplaneta$ (cockroach) is a triploblastic,coelomate arthropod.
Therefore,the correct answer is Sea Anemone.

(A) In $Hydra$,the endoderm consists of nutritive-muscular cells (also known as nutritive cells).
These cells are responsible for both digestion and movement of food particles within the gastrovascular cavity.
They possess flagella to create currents in the fluid for mixing food and pseudopodia to engulf food particles via phagocytosis.

(B) $Hydra$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
It possesses an incomplete digestive system with a single opening,the mouth (hypostome),which serves for both ingestion and egestion.
Undigested food residues are egested through the mouth.
Nitrogenous wastes,such as ammonia,are excreted primarily through the general body surface (body wall) via simple diffusion.
Therefore,the correct combination is mouth and body wall.

(B) . In $Hydra$,there is no specialized circulatory system or blood. Respiration occurs through the process of diffusion,where gases are exchanged directly between individual body cells and the surrounding water.

(D) The sea fan,scientifically known as $Gorgonia$,belongs to the phylum $Coelenterata$ (also known as $Cnidaria$).
These organisms are aquatic,mostly marine,sessile or free-swimming,and radially symmetrical animals.
They are characterized by the presence of cnidoblasts or cnidocytes on the tentacles and the body,which are used for anchorage,defense,and capturing prey.

(C) Sea anemone (scientific name: $Adamsia$) belongs to the phylum $Coelenterata$ (also known as $Cnidaria$).
These organisms are aquatic,mostly marine,sessile or free-swimming,and radially symmetrical animals.
They are characterized by the presence of cnidoblasts or cnidocytes (stinging cells) on the tentacles and the body,which are used for anchorage,defense,and capturing prey.

(B) Corals are marine invertebrates that belong to the phylum $Coelenterata$, also known as $Cnidaria$.
These organisms secrete calcium carbonate to form hard, stony structures known as coral reefs.
They exhibit radial symmetry and possess specialized stinging cells called cnidoblasts or cnidocytes, which are characteristic of this phylum.