Phylum-Coelenterata (Cnideria) Questions in English

(A) Sea fan $(Gorgonia)$ is a marine organism that belongs to the phylum $Coelenterata$ (also known as $Cnidaria$).
It is characterized by the presence of cnidoblasts and a radial symmetry,which are diagnostic features of this phylum.

(B) $Hydra$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
It lacks a specialized circulatory system for the transport of nutrients and gases.
Instead,it possesses a central body cavity known as the gastrovascular cavity (or coelenteron).
This cavity is lined by endoderm and is responsible for both digestion and the distribution of nutrients throughout the body,effectively compensating for the absence of a circulatory system.

(D) Nematoblasts (also known as $cnidoblasts$) are specialized cells found in $Hydra$.
They are sensory in nature,as they respond to external stimuli.
They contain a complex structure called the nematocyst apparatus,which is used for prey capture,offence,and defence.

(B) $Physalia$ (class $Hydrozoa$) is commonly known as the '$Portuguese\; man\; of\; war$'.
It belongs to the phylum $Cnidaria$ (also known as $Coelenterata$).

(D) The nematocyst of $Hydra$ is filled with a poisonous fluid known as hypnotoxin.
This substance is a complex mixture of proteins and phenols.
The nematocyst serves as a specialized organelle for offense,defense,food capture,anchorage,and locomotion in $Hydra$.

(A) The level of organization in animals is classified as cellular,tissue,organ,or organ-system level.
$1$. Cellular level: Seen in Porifera.
$2$. Tissue level: Seen in Coelenterata (Cnidaria) and Ctenophora.
$3$. Organ level: Seen in Platyhelminthes.
$4$. Organ-system level: Seen in Aschelminthes,Annelida,Arthropoda,Mollusca,Echinodermata,Hemichordata,and Chordata.
Since Coelenterata exhibits the tissue level of organization,option $A$ is the correct answer.

(A) The phylum $Coelenterata$ (also known as $Cnidaria$) is characterized by the presence of specialized stinging cells called $Nematocysts$ (or $Cnidoblasts$).
These cells are used for anchorage,defense,and the capture of prey.
$Polymorphism$ is also seen in some cnidarians,but $Nematocysts$ are the defining diagnostic feature of the entire phylum.
$Flame$ $cells$ are characteristic of the phylum $Platyhelminthes$ (excretion).
$Choanocytes$ are characteristic of the phylum $Porifera$ (sponges).

(A) Cnidoblasts are specialized stinging cells found in the phylum $Cnidaria$.
They serve several critical functions for the organism:
$1$. Capture of prey: Cnidoblasts contain a nematocyst that can coil around or penetrate the prey to capture it.
$2$. Defense: They protect the cnidarian by paralyzing or killing potential predators or threats using toxins and spines.
$3$. Anchorage: Cnidoblasts secrete sticky substances that help the organism attach to surfaces for locomotion or stability.
Digestion of food is performed by the gastrovascular cavity and intracellular digestion within the cells lining the cavity,not by cnidoblasts.
Therefore,digestion of food is not a function of cnidoblasts.

(B) Coelenterates (Phylum $Cnidaria$) exhibit radial symmetry.
In radially symmetric animals,any plane passing through the central axis of the body divides the organism into two identical halves.

(C) Digestion in phylum $Cnidaria$ (coelenterates) is both extracellular and intracellular.
Firstly,extracellular digestion occurs within the gastrovascular cavity.
Subsequently,intracellular digestion takes place within the gastrodermal cells.

(C) Metagenesis (alternation of generation) is a phenomenon observed in certain cnidarians where the organism exists in two distinct body forms: the sessile,cylindrical $polyp$ form and the free-swimming,umbrella-shaped $medusa$ form.
In this process,polyps produce medusae asexually,and medusae produce polyps sexually.
Among the given options,$Physalia$ (Portuguese man-of-war) is a member of the class $Hydrozoa$ that exhibits this phenomenon.
$Hydra$ exists only in the polyp form,while $Adamsia$ and $Meandrina$ exist primarily in the polyp form.

(B) Cnidarians (phylum $Cnidaria$) are exclusively aquatic animals,mostly marine. They are not found in terrestrial habitats.
They exhibit tissue level of organization.
They can be sessile (e.g.,$Hydra$) or free-swimming (e.g.,$Aurelia$).
They are diploblastic animals,meaning their body is derived from two embryonic layers: ectoderm and endoderm.

(C) $Cnidarians$ are ammonotelic and possess an incomplete digestive system,which has a single opening for both the entry of food and the exit of undigested waste. Nitrogenous waste materials,such as ammonia,are removed from the body surface via diffusion through the body wall.

(B) The epidermis of $Hydra$ contains several specialized cell types.
$1$. Interstitial cells: These are totipotent cells found in both the epidermis and gastrodermis,capable of differentiating into various cell types.
$2$. Cnidoblasts (or Cnidocytes): These are specialized stinging cells that contain nematocysts. They are exclusively found in the epidermis of cnidarians and are a characteristic feature of the phylum $Cnidaria$.
$3$. Sensory cells: These are found in the epidermis,but similar sensory structures are also present in other animal phyla.
$4$. Germ cells: These are derived from interstitial cells and are found in the epidermis during the reproductive phase,but they are not restricted to the epidermis in all contexts.
Since $Cnidoblasts$ are the unique and characteristic cells found only in the epidermis of cnidarians,the correct answer is $B$ only.

(C) Obelia (sea fur) belongs to the class $Hydrozoa$,phylum $Cnidaria$.
$1$. After fertilization,a ciliated free-swimming larva called the planula larva is formed ($A$ is correct).
$2$. $Obelia$ exhibits alternation of generations,also known as metagenesis,where the polyp stage reproduces asexually and the medusa stage reproduces sexually ($B$ is correct).
$3$. The medusae of $Obelia$ possess a true velum (a shelf-like fold of tissue),which makes them 'craspedote' medusae,not 'acraspedote' ($C$ is incorrect).
$4$. The medusoid stage of $Obelia$ contains statocysts,which are sensory organs for balance ($D$ is correct).
Therefore,the correct characteristics are $A, B$,and $D$.

(A) An atoll reef is also called a coral island or lagoon island,which is a circular or horse shoe-shaped reef that encircles a lagoon but does not enclose an island.
It may be complete or broken by a number of channels.
$e.g.$ - Lakshadweep and Maldive islands in the Indian Ocean.

(D) The correct answer is both $(a)$ and $(b)$.
Locomotory structures do not necessarily have to be different from those involved in other types of movements.
For example,in $Paramecium$,cilia help in the movement of food through the cytopharynx and also in locomotion.
Similarly,$Hydra$ can use its tentacles for capturing its prey and also for locomotion (somersaulting).
Humans use limbs for changes in body postures as well as for locomotion.

(N/A) $\rightarrow$ The cnidarians or coelenterates that exist in both polyp and medusa forms exhibit a phenomenon called alternation of generation,known as metagenesis.
In this process,polyps produce medusae asexually,and medusae produce polyps sexually.
For example,$Obelia$.

(N/A) $Polyp$ is a body form of $Cnidaria$ (coelenterates) that is sessile and cylindrical in shape.
Examples include $Hydra$ and $Adamsia$ (sea anemone).
It is typically attached to a substrate and may reproduce asexually.

(N/A) Medusa is a free-swimming,umbrella-shaped body form found in the phylum Cnidaria (Coelenterata).
Examples include $Aurelia$ (jellyfish).
It is characterized by a mouth directed downwards and is primarily involved in sexual reproduction.

(B) $\rightarrow$ Location: Stinging cells or cnidoblasts are present on the ectoderm of the tentacles and the body wall of organisms belonging to the phylum $Coelenterata$ (also known as $Cnidaria$).
$\rightarrow$ Function: These cells are specialized structures used for anchorage,capturing prey,and for offence and defence against predators.

(N/A) Metagenesis is the phenomenon of alternation of generation in certain cnidarians,where the asexual polyp form alternates with the sexual medusa form in the life cycle.
In this process,polyps produce medusae asexually,and medusae produce polyps sexually.
An example of an organism that exhibits metagenesis is $Obelia$.

(C) Cnidoblasts (also known as cnidocytes) are specialized cells characteristic of the phylum $Cnidaria$.
These cells contain stinging capsules called nematocysts.
They are primarily located on the tentacles and the body surface of cnidarians.
They are used for anchorage,defense,and the capture of prey.

(C) The image shows a cnidoblast or cnidocyte,which is a characteristic cell of the phylum Cnidaria (Coelenterata).
These cells contain a stinging capsule called a nematocyst.
Cnidoblasts are primarily found on the tentacles and the body surface of cnidarians.
They are used for anchorage,defense,and for the capture of prey.

(C) In Coelenterates (Cnidarians),digestion is both extracellular and intracellular.
$1$. Extracellular digestion occurs in the gastrovascular cavity,where enzymes are secreted onto the food.
$2$. Intracellular digestion occurs within the food vacuoles of the cells lining the gastrovascular cavity after the food particles are engulfed.

(C) In Phylum $Coelenterata$ (Cnidaria),the two basic body forms are $Polyp$ and $Medusa$.
$1$. $Polyp$ is a $sessile$ and $cylindrical$ form (e.g.,$Hydra$,$Adamsia$). It is produced by $asexual$ reproduction.
$2$. $Medusa$ is an $umbrella-shaped$ and $free-swimming$ form (e.g.,$Aurelia$ or jellyfish). It is produced by $sexual$ reproduction.
Matching the given statements:
- $Medusa$: $II$ $(Umbrella-shaped)$,$III$ $(Free-swimming)$,$VI$ ($Produced$ $by$ $sexual$ $reproduction$)
- $Polyp$: $I$ $(Sessile)$,$IV$ ($Produced$ $by$ $asexual$ $reproduction$),$V$ $(Cylindrical)$
Therefore,the correct matching is $Medusa$ $(II, III, VI)$ and $Polyp$ $(I, IV, V)$.

(D) The tentacles in $Cnidarians$ are specialized structures equipped with $cnidoblasts$ (stinging cells).
These tentacles perform multiple vital functions:
$1$. $Defense$: They protect the organism from predators.
$2$. $Anchorage$: They help the organism attach to the substrate or surface.
$3$. $Capture of prey$: They are used to paralyze and capture prey using the toxins released by the $cnidoblasts$.
Therefore, all the given options are correct functions of the tentacles.

(B) The organism that possesses an organized endoskeleton made of calcium carbonate is $Meandrina$,commonly known as the brain coral.
$Meandrina$ belongs to the phylum $Cnidaria$ (or $Coelenterata$).
Corals like $Meandrina$ secrete calcium carbonate $(CaCO_3)$ to form a hard,protective exoskeleton or endoskeleton structure.
$Adamsia$ is a sea anemone,$Sycon$ is a sponge (phylum $Porifera$),and $Ctenoplana$ belongs to the phylum $Ctenophora$.

(B) The phylum Coelenterata (Cnidaria) exhibits two basic body forms: Polyp and Medusa.
$1$. The first figure (left) represents the Medusa form,which is umbrella-shaped and free-swimming (e.g.,Aurelia).
$2$. The second figure (right) represents the Polyp form,which is cylindrical and sessile (e.g.,Hydra,Adamsia).
Therefore,the correct sequence is Medusa and Polyp.

(B) The correct matches are as follows:
$P$. Brain coral is $Meandrina$ $(II)$.
$Q$. Portuguese man-of-war is $Physalia$ $(V)$.
$R$. Sea anemone is $Adamsia$ $(I)$.
$S$. Hydra is $Hydra$ $(III)$.
$T$. Sea fan is $Gorgonia$ $(IV)$.
$U$. Sea pen is $Pennatula$ $(VI)$.
Therefore, the correct sequence is $(P-II), (Q-V), (R-I), (S-III), (T-IV), (U-VI)$.

(C) Corals are members of the phylum Coelenterata (Cnidaria) that secrete a hard exoskeleton composed of calcium carbonate $(CaCO_3)$. These structures form the basis of coral reefs.

(D) $Cnidoblasts$ (or $cnidocytes$) are specialized cells found in the phylum $Cnidaria$.
These cells contain stinging capsules called $nematocysts$.
The primary functions of $cnidoblasts$ are:
$1$. $Anchorage$: Helping the organism attach to a substrate.
$2$. $Defense$: Protecting the organism from predators.
$3$. $Capture \, of \, prey$: Paralyzing or killing prey using toxins.
Therefore, both $Anchorage$ and $Defense \, and \, capture \, of \, prey$ are correct functions.

(B) Cnidarians exhibit two basic body forms: the polyp and the medusa.
$Hydra$ exists only in the polyp form.
$Obelia$ and $Physalia$ exhibit both polyp and medusa forms (alternation of generation).
$Aurelia$ (jellyfish) exists primarily in the medusa form,and the polyp phase is absent or highly reduced in its life cycle.

(A) The central gastrovascular cavity is a characteristic feature of the phylum $Cnidaria$ (also known as $Coelenterata$).
$Adamsia$ (Sea anemone) belongs to the phylum $Cnidaria$ and possesses a central gastrovascular cavity with a single opening called the hypostome.
$Spongilla$ and $Sycon$ belong to the phylum $Porifera$,which lack a gastrovascular cavity.
$Taenia$ (Tapeworm) belongs to the phylum $Platyhelminthes$,which has an incomplete digestive system but lacks a true gastrovascular cavity as found in cnidarians.
Therefore,the correct option is $A$.

(C) Statement $(A)$ is correct: $Coelenterates$ (Cnidarians) are aquatic,mostly marine,sessile or free-swimming,and radially symmetrical.
Statement $(B)$ is correct: They possess a central gastro-vascular cavity with a single opening called the hypostome.
Statement $(C)$ is correct: Digestion in $Coelenterates$ is both extracellular and intracellular.
Statement $(D)$ is incorrect: $Sycon$,$Spongilla$,and $Euspongia$ are members of phylum $Porifera$,not $Coelenterata$.
Therefore,statements $(A), (B),$ and $(C)$ are correct.

(B) diffused nervous system is a primitive type of nervous system where nerve cells are distributed throughout the body in a net-like pattern,rather than being concentrated in a central brain or ganglia.
This type of nervous system is characteristic of the phylum $Cnidaria$ (e.g.,Hydra),where a nerve net is present beneath the epidermis to coordinate responses to stimuli.