Phylum-Coelenterata (Cnideria) Questions in English

(C) $Hydra$ and jellyfishes belong to the phylum $Cnidaria$ (also known as $Coelenterata$).
In these organisms,the cells performing the same function are arranged into tissues.
Therefore,they exhibit a tissue level of structural organization.

(C) The $Blind \text{ } sac$ body plan is characteristic of organisms that possess a single opening to the digestive tract, which serves as both the mouth for ingestion and the anus for egestion. This type of body plan is found in $Coelenterates$ (Cnidarians) and $Platyhelminthes$ (flatworms).

(B) $Hydra$ belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
Animals in this phylum exhibit radial symmetry,which means their body can be divided into identical halves by any plane passing through the central longitudinal axis.

(D) The body of a $Sea \text{ } Anemone$ (Phylum $Cnidaria$) exhibits radial symmetry. Specifically, it shows biradial symmetry, where the body can be divided into two similar halves by one or two vertical planes passing through the central axis. Therefore, the correct option is $D$.

(C) radially symmetrical and diploblastic animal belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
$Hydra$ is a classic example of a $Cnidarian$.
Roundworms $(Aschelminthes)$ are bilaterally symmetrical and triploblastic.
Earthworms $(Annelida)$ are bilaterally symmetrical and triploblastic.
Liver Flukes $(Platyhelminthes)$ are bilaterally symmetrical and triploblastic.
Therefore,the correct answer is $Hydra$.

(C) In the animal kingdom,organisms are classified based on their level of organization.
$1$. Sponges exhibit a cellular level of organization.
$2$. $Hydra$ (a member of Phylum $Cnidaria$) exhibits a tissue level of organization,where cells performing the same function are arranged into tissues.
$3$. Liver fluke (Phylum $Platyhelminthes$) and Starfish (Phylum $Echinodermata$) exhibit organ and organ-system levels of organization,respectively.
Therefore,tissue-level organization is characteristic of $Hydra$.

(B) The larva-like stage in the development of $Hydra$ is called the $Hydrula$.
It is a double-layered embryo that represents the early developmental stage of the organism.

(B) $Physalia$ colony is a tetramorphic colony because it consists of four types of zooids.
The zooids include:
$(i)$ $Gastrozooids$ for feeding.
$(ii)$ $Dactylozooids$ for defense.
$(iii)$ $Gonodendra$ for bearing male and female gonophores.
$(iv)$ $Gonopalpons$ for the protection of gonophores.

(B) $Hydra$ is a freshwater coelenterate (Cnidarian).
It exhibits only the polyp form and lacks the medusa stage in its life cycle.

(C) Polymorphism is a phenomenon where an organism exists in more than one morphological form,such as the presence of both polyp and medusa forms in a single life cycle or colony.
$Porpita$,$Vellela$,and $Physalia$ are colonial hydrozoans that exhibit polymorphism,consisting of different types of zooids (e.g.,gastrozooids,dactylozooids,gonozooids) within a single colony.
$Adamsia$ (sea anemone) belongs to the class $Anthozoa$. Members of this class exist only in the polyp form and do not exhibit polymorphism.

(A) Coelenterates (Cnidarians) lack a true body cavity or coelom between the body wall and the digestive tract.
Therefore,they are classified as $Acoelomate$ organisms.

(B) In the phylum $Cnidaria$ (also known as $Coelenterata$),organisms exhibit two basic body forms: the $polyp$ and the $medusa$.
$Anthozoa$ (e.g.,sea anemones) exist only in the $polyp$ form.
$Hydrozoa$ (e.g.,$Hydra$) typically exhibit both forms or are dominated by the $polyp$ form.
In the class $Scyphozoa$ (e.g.,jellyfish),the $medusa$ is the dominant form,and the $polyp$ stage is either highly reduced or entirely absent during their life cycle.
Therefore,the correct answer is $B$.

(C) The term 'sea stick' or 'sea pen' is commonly associated with members of the phylum $Coelenterata$ (also known as $Cnidaria$).
Specifically,organisms belonging to the order $Pennatulacea$ within this phylum are referred to as sea pens or sea sticks due to their feather-like or stick-like appearance.
Therefore,the correct group is $Coelenterata$.

(A) Polymorphism is a phenomenon where an organism exists in more than one morphological form within the same species.
$Physalia$,commonly known as the Portuguese man-o'-war,is a classic example of a polymorphic colonial coelenterate (Cnidarian).
It exhibits different types of zooids such as gastrozooids (for feeding),dactylozooids (for defense),and gonozooids (for reproduction) within a single colony.
$Fungia$ and $Hydra$ are not polymorphic in the same sense as $Physalia$.

(B) $Obelia$ exhibits an alternation of asexual and sexual phases,where both phases are diploid.
The asexual phase is represented by the polyp colony,while the sexual phase is represented by the medusa.
These two forms alternate in the life cycle of the organism.
Such a specific type of alternation between asexual and sexual phases is known as metagenesis.

(C) $Sea$ $cucumber$ is the common name of $Cucumaria$. It belongs to the phylum $Echinodermata$,not $Coelenterata$ (also known as $Cnidaria$).
$Sea$ $pen$ $(Pennatula)$,$Sea$ $feather$ ($Metridium$ or $Pennatula$ variants),and $Sea$ $fan$ $(Gorgonia)$ are all members of the phylum $Coelenterata$.

(B) Sea anemone (genus $Adamsia$) belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
Within this phylum,it is classified under the class $Anthozoa$.
$Anthozoa$ includes organisms that exist only in the polyp form and lack a medusa stage.
Therefore,the correct option is $B$.

(B) $Hydra$ is a freshwater coelenterate that exhibits a polyp body form.
It is commonly referred to as the 'freshwater polyp'.
In contrast,$Aurelia$ (jellyfish),$Obelia$,and $Physalia$ (Portuguese man-of-war) are primarily marine coelenterates.

(C) Corals are marine invertebrates that belong to the phylum $Cnidaria$ (also known as $Coelenterata$).
These organisms are characterized by the presence of cnidoblasts or cnidocytes (stinging cells) on their tentacles and body,which are used for anchorage,defense,and capturing prey.
Most corals secrete calcium carbonate to form a hard skeleton,which contributes to the formation of coral reefs.

(C) $Hydra$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
It is a predatory organism that feeds on small aquatic animals like $Daphnia$,$Cyclops$,and small insect larvae.
Since it captures and consumes other animals for nutrition,it is classified as a carnivorous organism.

(B) The correct answer is $B$. Choanocytes,also known as collar cells,are a characteristic feature of the phylum $Porifera$. They are specialized cells that line the interior of sponges and help in water circulation and feeding. In contrast,Coelenterates (Cnidarians) are characterized by the presence of a central gastrovascular cavity called the coelenteron,radial symmetry,and specialized stinging cells called nematoblasts (or cnidoblasts) for defense and prey capture.

(B) Jellyfish belongs to the class $Scyphozoa$ of the phylum $Coelenterata$ (also known as $Cnidaria$).
These organisms are characterized by a dominant medusa stage in their life cycle.

(D) The correct answer is $D$.
Specialized cells known as $Nematocysts$ (or $Cnidoblasts$) are a unique characteristic found exclusively in the phylum $Coelenterata$ (also known as $Cnidaria$).
These cells contain a stinging capsule and are primarily used for capturing prey,anchorage,and defense against predators.

(B) $Tubipora$ is commonly known as the organ pipe coral. It belongs to the phylum $Cnidaria$ (or $Coelenterata$). The name is derived from the arrangement of its calcareous tubes,which resemble the pipes of a musical organ.

(D) The 'Portuguese man-of-war' is the common name for $Physalia$ $physalis$.
It belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).
It is a colonial organism consisting of specialized individuals called zooids that perform different functions,making it a polymorphic colony.

(A) $Corallium rubrum$ is the precious red coral of commerce.
It is highly valued because it is used for making jewellery.

(C) The phylum $Coelenterata$ (also known as $Cnidaria$) is characterized by a $Tissue$ level of organization.
In this level,the cells performing the same function are arranged into tissues,which is a step higher than the $Cellular$ level of organization found in phylum $Porifera$.
They do not possess true organs or organ systems.

(A) The body cavity of $Hydra$ is known as the coelenteron or gastrovascular cavity.
It is surrounded by the body wall.
The mouth leads directly into this cavity,which is responsible for both digestion and circulation of nutrients.

(D) The $Pneumatophore$ is a gas-filled float or bladder found in certain colonial cnidarians like $Physalia$ (Portuguese man-o'-war).
It acts as a hydrostatic organ that allows the organism to float on the surface of the water.

(A) The characteristic larva found in the life cycle of many coelenterates (Cnidarians),such as $Obelia$,is known as the $Planula$ larva.
It is a ciliated,free-swimming larva that eventually settles on a substrate to develop into a polyp.

(B) An $Atoll$ is a ring-shaped coral reef,including a coral rim that encircles a lagoon partially or completely.
It is formed when a volcanic island sinks or erodes,leaving behind a ring of coral that continues to grow upwards,surrounding a central shallow lake or lagoon.

(D) The life cycle of $Hydra$ is direct,meaning it does not involve any larval stage. The offspring develop directly into miniature adults. Therefore,none of the options provided represent the larva of $Hydra$.

(D) Corals belong to the phylum $Cnidaria$ (also known as $Coelenterata$).
They exhibit a $polypoid$ body form,which is sessile and cylindrical.
Corals can exist as solitary individuals or in colonial forms.
Many corals secrete calcium carbonate skeletons,which can grow into massive,branched,or complex structures over time.
Therefore,all the given statements are correct.

(C) In coelenterates,the body organization is simple and lacks a specialized circulatory or respiratory system. Therefore,${O_2}$ is carried to various tissues directly from the surrounding water through the general body surface (integument) by the process of diffusion.

(A) The phylum Coelenterata,also known as Cnidaria,is divided into three main classes: Hydrozoa,Scyphozoa,and Anthozoa.
$Obelia$ is a colonial marine organism that exhibits metagenesis (alternation of generations).
It belongs to the class Hydrozoa,which is characterized by the presence of both polyp and medusa forms in its life cycle.

(C) In $Hydra$,the ovary is a temporary structure that develops from the interstitial cells.
During the process of oogenesis within the ovary,only a single mature ovum is produced.
This is because the developing oocyte consumes the other surrounding cells to accumulate nutrients,ensuring the survival of the single egg.

(D) $Sea \text{ } pen$ $(Pennatula)$ is a colonial coelenterate belonging to the phylum $Cnidaria$ (also known as $Coelenterata$).
$Sea \text{ } cow$ is a mammal $(Sirenia)$.
$Sea \text{ } horse$ is a bony fish $(Hippocampus)$.
$Sea \text{ } cucumber$ is an echinoderm $(Holothuroidea)$.

(D) $Hydra$ possesses a primitive nervous system consisting of a nerve net composed of interconnected neurons.
Sensory cells are distributed throughout the epidermis to detect environmental stimuli.
$Nematocytes$ (or $Cnidocytes$) are specialized cells that contain stinging organelles and also function as sensory receptors to trigger the discharge of the nematocyst in response to external stimuli.
Therefore,all these structures contribute to the reception of impulses and stimuli in $Hydra$.

(A) In the class $Hydrozoa$,many species exhibit metagenesis or alternation of generations,where both polyp and medusa forms are present in the life cycle of the same animal.
For example,in $Obelia$,the polyp stage is sessile and asexual,while the medusa stage is free-swimming and sexual.
Therefore,the correct option is $A$.

(B) The class $Anthozoa$ belongs to the phylum $Cnidaria$ and includes corals and sea anemones.
$Fungia$ is a genus of mushroom corals that belongs to the class $Anthozoa$.
$Aurelia$ (jellyfish) belongs to the class $Scyphozoa$.
$Stercularia$ (often referred to as $Sertularia$) belongs to the class $Hydrozoa$.
$Dugesia$ (planaria) belongs to the phylum $Platyhelminthes$.

(B) $Coelenterata$ (also known as $Cnidaria$) animals are diploblastic,meaning they possess two germ layers: an outer epidermis and an inner gastrodermis.
Between these two layers,a non-cellular,jelly-like substance called $Mesogloea$ is present,which provides structural support.

(D) Statocysts are specialized balancing organs found in the medusa stage of $Obelia$.
These organs help the organism maintain equilibrium and orientation in the water column.

(C) The 'Ephyra' larva is a characteristic larval stage in the life cycle of the class Scyphozoa,commonly known as jellyfish.
Specifically,it is the free-swimming larval form produced by the strobilation of the scyphistoma polyp in the life cycle of $Aurelia$ (moon jelly).
Therefore,the correct option is $C$.

(B) $Hydra$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
These organisms are diploblastic and lack a true skeleton,whether internal or external.
Therefore,$Hydra$ does not possess an endoskeleton.

(D) Diploblastic organisms are those that possess two germ layers: an outer ectoderm and an inner endoderm.
$Acoelomate$ refers to animals that lack a body cavity (coelom).
$Planaria$ (Platyhelminthes) is triploblastic and acoelomate.
$Ascaris$ (Aschelminthes) is triploblastic and pseudocoelomate.
$Rotifer$ is triploblastic and pseudocoelomate.
$Sea \text{ } anemone$ (Cnidaria) is diploblastic and acoelomate.
Therefore, the correct option is $D$.

(A) The $Sea$ $anemone$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
It is a marine, sessile organism that is completely non-parasitic and lives as a predator or scavenger.
In contrast, $Leech$ (phylum $Annelida$) is an ectoparasite, $Tapeworm$ (phylum $Platyhelminthes$) is an endoparasite, and $Mosquito$ (phylum $Arthropoda$) is an ectoparasite that feeds on blood.

(D) $Cnidoblasts$ $(nematoblasts)$ are specialized and modified interstitial cells that are found exclusively in $Cnidaria$ (coelenterates).
These cells contain stinging capsules used for defense,offense,and capturing prey.
Vertebrates do not possess $cnidoblasts$; instead,they have complex organ systems and specialized tissues.

(B) In the phylum $Coelenterata$ (also known as $Cnidaria$),the nervous system is present in its most primitive form.
It consists of a diffuse network of nerve cells (neurons) scattered throughout the body.
However,these nerve cells are not organized into true nerves,ganglia,or a central nervous system.
Therefore,while individual nerve cells are present to conduct impulses,they do not form organized nerve cords or nerves.

(A) Segmentation (metamerism) is a characteristic feature where the body is divided into repeating units called metameres.
$1$. $Hydra$ belongs to the phylum $Cnidaria$ (Coelenterata),which is characterized by a diploblastic,radially symmetrical body without any true segmentation.
$2$. $Earthworm$ $(Annelida)$,$Cockroach$ $(Arthropoda)$,and $Centipede$ $(Arthropoda)$ all exhibit true segmentation in their body structure.
Therefore,$Hydra$ is the correct answer.