Phylum-Chordata Questions in English

(C) In vertebrates,the notochord is present during the embryonic period. It is replaced by a cartilaginous or bony vertebral column in the adult. Therefore,the transformation occurs during the embryonic development phase.

(C) In the subphylum Urochordata (also known as Tunicata),the notochord is present only in the larval tail. As the larva undergoes metamorphosis into an adult,the notochord disappears. Therefore,the presence of a notochord in the larval tail is a characteristic feature of Urochordata.

(B) The phylum Chordata is classified into three subphyla: Urochordata (or Tunicata),Cephalochordata,and Vertebrata.
According to the provided chart,the subphyla are listed under Chordata. The third one is Vertebrata.
Therefore,$a$ and $b$ represent Urochordata and Cephalochordata respectively.

(C) $Salpa$ is a genus of tunicate (tunicates are also known as Urochordates).
In the phylum Chordata,the subphylum Urochordata (or Tunicata) includes organisms where the notochord is present only in the larval tail.
$Salpa$ belongs to the class Thaliacea within the subphylum Urochordata.
Therefore,the correct option is $C$.

(C) $A:$ Amphioxus (Branchiostoma) belongs to the subphylum Cephalochordata. While it possesses a notochord throughout its life,it lacks a vertebral column,thus it is not a vertebrate. Therefore,statement $A$ is true.
$R:$ Amphioxus is a classic example of a protochordate (cephalochordate). It possesses a notochord,a dorsal hollow nerve cord,and pharyngeal gill slits,which are the defining characteristics of the phylum Chordata. Therefore,statement $R$ is false.

(C) The phylum Chordata is divided into three subphyla: Urochordata,Cephalochordata,and Vertebrata.
In subphylum Urochordata (also known as Tunicata),the notochord is present only in the larval tail and disappears in the adult stage.
Examples of Urochordata include $Ascidia$,$Salpa$,and $Doliolum$.
$Amphioxus$ (Cephalochordata) retains the notochord throughout its entire life,extending from head to tail.
Therefore,both $Ascidia$ and $Salpa$ are urochordates that possess a notochord only during the larval stage.

(A) Invertebrates are characterized by the absence of a notochord. Their nervous system is solid,double,and ventral,often containing ganglia. In contrast,chordates have a dorsal,hollow,and single nerve cord. The digestive tract in invertebrates is typically located on the ventral side of the nerve cord,whereas in chordates,it is located on the ventral side of the notochord. Therefore,the statement that the digestive tract is located on the dorsal side of the nerve cord is incorrect for invertebrates.

(D) The fundamental characteristics of Chordates include the presence of a notochord,a dorsal hollow nerve cord,and paired pharyngeal gill slits.
In Chordates,the central nervous system is dorsal,hollow,and single,not solid.
In contrast,non-chordates (invertebrates) typically possess a ventral,solid,and double nerve cord.
Therefore,the statement that their nervous system is solid is incorrect for Chordates.

(C) The correct matching is as follows:
$(1)$ Urochordata (Tunicata): In these organisms, the notochord is present only in the larval tail.
$(2)$ Cephalochordata: In these organisms, the notochord extends from head to tail region and is persistent throughout their life.
$(3)$ Vertebrata: In vertebrates, the notochord is present during the embryonic period and is replaced by a cartilaginous or bony vertebral column in the adult.
$(4)$ Chordata: The phylum Chordata is characterized by the presence of a notochord, which is a rod-like structure of mesodermal origin.
Therefore, the correct sequence is $(1-d), (2-c), (3-b), (4-a)$.

(C) The correct answer is $C$.
$A$: In Ascidians (Urochordata),the notochord is present only in the larval tail. This statement is correct.
$B$: In adult frogs (Vertebrata),the notochord is replaced by a vertebral column. This statement is correct.
$C$: Humans are chordates. In all chordates,the notochord is present at least during the early embryonic stage. Therefore,saying it is absent from the very beginning in humans is incorrect.
$D$: In Amphioxus (Cephalochordata),the notochord extends from the head to the tail region and persists throughout their life. This statement is correct.

(D) Non-chordates are characterized by the following features:
$1$. The central nervous system is ventral,solid,and double.
$2$. Pharyngeal gill slits are absent.
$3$. The heart,if present,is dorsal.
$4$. Post-anal tail is absent.
Comparing these with the given statements:
$(I)$ Correct: Non-chordates have a ventral,solid,and double nerve cord.
$(II)$ Correct: Gill slits are absent in non-chordates.
$(III)$ Incorrect: In non-chordates,the heart is dorsal (if present),whereas it is ventral in chordates.
$(IV)$ Correct: Post-anal tail is absent in non-chordates.
Therefore,statements $(I), (II),$ and $(IV)$ are correct.

(B) The notochord is a flexible,rod-like structure that serves as a defining characteristic of the phylum $Chordata$.
During embryonic development,the three primary germ layers are formed: $Ectoderm$,$Mesoderm$,and $Endoderm$.
The notochord is formed from the $Mesoderm$ layer during the process of gastrulation.
Therefore,the correct option is $B$.

(D) In the $Phylum$ $Chordata$,specifically within the $Subphylum$ $Urochordata$ (also known as $Tunicata$),the body of the adult organism is typically not divided into distinct regions like head,thorax,and abdomen. However,in certain $Chordates$ like $Ascidia$ (a sea squirt),the body is often described as being organized into a head and a trunk region. $Cockroach$ belongs to $Phylum$ $Arthropoda$ and its body is divided into head,thorax,and abdomen. $Toad$ belongs to $Amphibia$ and its body is divided into head and trunk. Given the context of typical biological classification questions,$Ascidia$ is the correct answer as it represents a chordate where the body plan is simplified into these two primary regions.

(C) $Branchiostoma$ (also known as $Amphioxus$ or lancelet) belongs to the subphylum $Cephalochordata$.
In $Cephalochordata$,the notochord extends from head to tail region and is persistent throughout their life.
$Cyclostomata$ are jawless vertebrates.
$Chondrichthyes$ are cartilaginous fishes.
$Osteichthyes$ are bony fishes.

(B) In the animal kingdom,the evolution of excretory systems shows a progression from simple structures to complex organs.
In $Chordata$,the presence of kidneys as specialized excretory organs is a defining characteristic.
While other phyla like $Mollusca$ and $Echinodermata$ have excretory structures (such as nephridia or water vascular systems),the true kidney as a complex organ for filtration and excretion is first observed in the phylum $Chordata$.

(B) The frog belongs to the Kingdom $Animalia$,Phylum $Chordata$,Class $Amphibia$,Order $Anura$,Genus $Rana$,and Species $tigrina$.
$Chordata$ is the phylum because frogs possess a notochord at some stage of their life cycle,a dorsal hollow nerve cord,and pharyngeal gill slits.

(C) The fundamental characteristics of $Phylum-Chordata$ include the presence of a notochord,a dorsal hollow nerve cord,and a post-anal tail at some stage of their life cycle.
Among the given options,the post-anal tail is a unique diagnostic feature of chordates.
While pharyngeal gill slits are also a characteristic,the post-anal tail is a defining feature that distinguishes chordates from non-chordates.

(B) All vertebrates belong to the phylum $Chordata$.
Key characteristics of chordates include the presence of a notochord,a dorsal hollow nerve cord,and pharyngeal gill slits at some stage of their life cycle.
While not all vertebrates have a renal portal system or a four-chambered heart (e.g.,fish have a two-chambered heart),the presence of a dorsal,hollow,central nervous system is a fundamental diagnostic feature of all vertebrates.

(D) The phylum $Chordata$ is characterized by the presence of a notochord,a dorsal hollow nerve cord,and paired pharyngeal gill slits at some stage of their life cycle. The notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals. Therefore,the presence of a notochord is the defining feature of all chordates.

(A) Vertebrates are a subphylum of Chordata characterized by the presence of a vertebral column.
All vertebrates possess a cranium (brain box) that protects the brain,which is why they are also known as Craniata.
Option $A$ is correct because the presence of a cranium is a defining feature of all vertebrates.
Options $B$,$C$,and $D$ are not universal characteristics; for example,cyclostomes lack jaws and paired appendages,and many vertebrates do not have a distinct neck or a body covered by an exoskeleton.

(B) Metamerism (or true segmentation) is a characteristic feature where the body is externally and internally divided into segments with a serial repetition of at least some organs.
In the animal kingdom,true metamerism is primarily observed in three phyla: $Annelida$,$Arthropoda$,and $Chordata$.
While $Annelida$ and $Arthropoda$ show prominent external and internal segmentation,$Chordata$ (specifically in vertebrates) exhibit metamerism in their internal structures such as muscles,nerves,and vertebral column.

(D) The presence of a post-anal tail is one of the fundamental diagnostic characteristics of the Phylum $Chordata$.
Among the given options, the $Earthworm$ (Annelida), $Scorpion$ (Arthropoda), and $Lower$ invertebrates do not possess a post-anal tail.
A $Snake$ is a member of the Class $Reptilia$, which belongs to the Phylum $Chordata$.
Therefore, the $Snake$ possesses a post-anal tail during its life cycle.

(A) The phylum $Chordata$ is characterized by the presence of a notochord,a dorsal hollow nerve cord,and paired pharyngeal gill slits at some stage of their life cycle.
In all chordates,the notochord is present during the embryonic stage. It is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development.

(A) Chordates are a group of animals that include fish,amphibians,reptiles,birds,and mammals.
The defining characteristics of the chordate nervous system include a central nervous system consisting of a brain and a hollow,dorsal nerve cord.
Additionally,chordates possess highly developed sensory receptors to detect environmental stimuli.
In contrast,fused ganglia are characteristic of annelids and arthropods,tympana are found in insects like grasshoppers,and nerve nets are characteristic of cnidarians like Hydra.

(A) Acraniata (also known as Protochordata) is a group of chordates that lack a distinct cranium (brain box) and a vertebral column.
These organisms are exclusively marine and lack a well-defined head region,which is why they are often referred to as 'acraniates'.
Since the absence of a cranium is directly linked to the lack of a developed head region in these primitive chordates,the Reason correctly explains the Assertion.

(N/A) The characteristic features of the phylum $Chordata$ include the presence of a notochord and paired pharyngeal gill slits.
In the sub-phylum $Vertebrata$, the notochord present in the embryo is replaced by a cartilaginous or bony vertebral column in the adult.
Since all vertebrates possess a vertebral column (which is a modified notochord), they are classified as chordates.
However, some chordates, such as those in the sub-phyla $Urochordata$ and $Cephalochordata$, possess a notochord throughout their life or only in the larval stage but do not develop a vertebral column.
Therefore, it is correct to state that all vertebrates are chordates, but all chordates are not vertebrates.

(A) $\rightarrow$ The notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals.
$\rightarrow$ Animals that possess a notochord at any stage of their life cycle are classified as chordates.
$\rightarrow$ Animals that do not form this structure are classified as non-chordates,which include phyla from Porifera to Echinodermata.

(N/A) $\rightarrow$ Animals belonging to phylum Chordata are fundamentally characterised by the presence of a notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits.
$\rightarrow$ These are bilaterally symmetrical, triploblastic, and coelomate animals with an organ-system level of organisation.
$\rightarrow$ They possess a post-anal tail and a closed circulatory system.
$\rightarrow$ Phylum Chordata is divided into three subphyla: Urochordata (or Tunicata), Cephalochordata, and Vertebrata.
$\rightarrow$ Protochordates:
$\rightarrow$ Subphyla Urochordata and Cephalochordata are often referred to as protochordates and are exclusively marine.
$\rightarrow$ In Urochordata, the notochord is present only in the larval tail, while in Cephalochordata, it extends from the head to the tail region and is persistent throughout their life.
$\rightarrow$ Examples of Urochordata: Ascidia, Salpa, Doliolum.

(N/A) The fundamental characteristics of Phylum Chordata include the following four features:
$1$. Notochord: $A$ flexible,rod-like structure providing support.
$2$. Dorsal hollow nerve cord: $A$ nerve cord located dorsally to the notochord.
$3$. Pharyngeal gill slits: Paired openings in the pharyngeal region.
$4$. Post-anal tail: $A$ muscular extension of the body beyond the anal opening.
The provided diagram illustrates these four key diagnostic features of chordates.

(N/A)

Non-Chordata	Chordata
$(1)$ Notochord is absent.	$(1)$ Notochord is present.
$(2)$ Digestive tract is dorsal to the nerve cord.	$(2)$ Digestive tract is ventral to the nerve cord.
$(3)$ Pharyngeal gill slits are absent.	$(3)$ Pharyngeal gill slits are present.
$(4)$ Blood circulatory system is open,closed,or absent.	$(4)$ Blood circulatory system is always closed.
$(5)$ Nervous system is solid,nerve cord is double,ventral,and ganglionated.	$(5)$ Nervous system is hollow,nerve cord is single,dorsal,and without ganglia.
$(6)$ Animals are cold-blooded (poikilothermic).	$(6)$ Animals can be cold-blooded or warm-blooded (homeothermic).
$(7)$ Post-anal tail is absent.	$(7)$ Post-anal tail is present.

(N/A) The phylum $Chordata$ is divided into three subphyla:
$1$. $Urochordata$ (Tunicata): The notochord is present only in the larval tail,e.g.,$Ascidia$.
$2$. $Cephalochordata$: The notochord extends from head to tail region and is persistent throughout their life,e.g.,$Amphioxus$.
$3$. $Vertebrata$: The notochord is replaced by a cartilaginous or bony vertebral column in the adult,e.g.,from $Cyclostomata$ to $Mammalia$.

(N/A) Animals that possess a notochord throughout their life are classified under the subphylum Cephalochordata.
Characteristics of Cephalochordata:
- They are exclusively marine animals.
- They are primitive chordates.
- The notochord persists throughout their entire life cycle and extends from the head to the tail region.
- Example: $Branchiostoma$ (also known as Amphioxus or Lancelet).
Note: Urochordata (Tunicata) are also primitive chordates,but in them,the notochord is present only in the larval tail stage and disappears in the adult stage.

(B) The subphylum $Vertebrata$ is characterized by the following features:
$1$. Members possess a notochord during the embryonic period.
$2$. The notochord is replaced by a cartilaginous or bony vertebral column in the adult stage.
$3$. All vertebrates are chordates,but all chordates are not vertebrates.
$4$. They possess a ventral muscular heart with two,three,or four chambers.
$5$. They have kidneys for excretion and osmoregulation.
$6$. They possess paired appendages which may be fins or limbs.

(N/A) $\rightarrow$ The members of subphylum $Vertebrata$ possess a notochord during the embryonic period.
$\rightarrow$ The notochord is replaced by a cartilaginous or bony vertebral column in the adult.
$\rightarrow$ Since all vertebrates possess a vertebral column,they are classified as chordates. However,other chordates,such as those in subphyla $Urochordata$ and $Cephalochordata$,possess a notochord but lack a vertebral column. Thus,all vertebrates are chordates,but all chordates are not vertebrates.

(D) The subphylum $Vertebrata$ is divided into two divisions based on the presence or absence of jaws:
$1$. $Agnatha$ (jawless vertebrates): Includes the class $Cyclostomata$.
$2$. $Gnathostomata$ (jawed vertebrates): This division is further divided into two superclasses:
- $Pisces$ (bearing fins): Includes classes $Chondrichthyes$ and $Osteichthyes$.
- $Tetrapoda$ (bearing limbs): Includes classes $Amphibia$,$Reptilia$,$Aves$,and $Mammalia$.
Therefore,the classification involves both the primary division into $Agnatha$ and $Gnathostomata$ and the subsequent division of $Gnathostomata$ into superclasses $Pisces$ and $Tetrapoda$.

(A) $Amphioxus$ (also known as $Branchiostoma$ or lancelet) is a primitive chordate belonging to the subphylum $Cephalochordata$.
It possesses specialized excretory structures known as flame cells (or protonephridia) which are primarily involved in excretion and osmoregulation.
While flame cells are characteristic of flatworms $(Platyhelminthes)$,they are also found in the larvae of certain chordates like $Amphioxus$.

(N/A) $(i)$ Cephalochordata: These are chordates in which the notochord extends from head to tail region and is persistent throughout their life. Examples include $Branchiostoma$ (Amphioxus or Lancelet).
$(ii)$ Pseudocoelomates: These are animals in which the body cavity is not lined by mesoderm; instead,the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called a pseudocoel,and the animals possessing them are called pseudocoelomates. Example: $Aschelminthes$ (Roundworms).

(N/A)

Direct development	Indirect development
$(1)$ In this type of development,there are no larval,nymphal,or other intermediate stages in the life cycle between the egg (or birth) and the adult.	$(1)$ In this type of development,the organism passes through one or more larval or nymphal stages before reaching the adult form.
$(2)$ Example: Mammals,birds,and reptiles.	$(2)$ Example: Echinoderms,many insects (arthropods),and amphibians.

(N/A) Two-chambered heart: Present in fishes. It consists of one atrium and one ventricle,where oxygenated and deoxygenated blood mix.
$(b)$ Three-chambered heart: Present in amphibians. The atrium is divided into right and left halves,but the ventricle is undivided,leading to the mixing of blood.
$(c)$ Incomplete four-chambered heart: Present in most reptiles (except crocodiles). The ventricle is partially divided by an incomplete septum.
$(d)$ Four-chambered heart: Present in birds,mammals,and crocodiles. Both atria and ventricles are completely divided,preventing the mixing of oxygenated and deoxygenated blood.

(N/A)

Notochord	Nerve cord
$(1)$ It is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals.	$(1)$ It is an ectodermally derived structure,present on the dorsal or ventral side in all animals.
$(2)$ It may exist throughout life,only during embryonic stages,or may be replaced by the vertebral column.	$(2)$ It remains present throughout the life of the animal.

(N/A)

Chordates	Non-chordates
$(1)$ Notochord is present in at least one stage of the life cycle.	$(1)$ Notochord is absent.
$(2)$ Pharyngeal gill slits are present.	$(2)$ Pharyngeal gill slits are absent.
$(3)$ Post-anal tail is present.	$(3)$ Post-anal tail is absent.
$(4)$ Heart is ventrally located.	$(4)$ Heart is dorsally located (if present).
$(5)$ Central nervous system is dorsally located and is hollow.	$(5)$ Central nervous system is ventrally located and is solid.

The schematic sketch of a chordate showing these features is provided in the reference image.

(N/A) The three major differences between chordates and non-chordates are as follows:
$1$. Notochord: Chordates possess a notochord at some stage of their life cycle,whereas non-chordates lack a notochord.
$2$. Central Nervous System: In chordates,the central nervous system is dorsal,hollow,and single. In non-chordates,it is ventral,solid,and double.
$3$. Pharyngeal Gill Slits: Chordates exhibit pharyngeal gill slits at some stage of development,which are absent in non-chordates.
Schematic sketch description: $A$ chordate body plan includes a dorsal hollow nerve cord,a notochord located below the nerve cord,a post-anal tail,and pharyngeal gill slits in the pharyngeal region.

(A) Statement $(a)$ is incorrect because in $Urochordata$ (Tunicata),the notochord is present only in the larval tail.
Statement $(b)$ is correct because in $Vertebrata$,the notochord is replaced by a cartilaginous or bony vertebral column in the adult.
Statement $(c)$ is correct as a dorsal,hollow central nervous system is a fundamental characteristic of chordates.
Statement $(d)$ is incorrect because $Chordata$ is divided into $3$ subphyla: $Urochordata$ (or $Tunicata$),$Cephalochordata$,and $Vertebrata$. $Hemichordata$ is a separate phylum.
Therefore,statements $(b)$ and $(c)$ are true.

(D) The phylum Chordata is characterized by the presence of a notochord,a dorsal hollow nerve cord,and paired pharyngeal gill slits.
Statement $(a)$ is correct: In Cephalochordata,the notochord extends from head to tail region and is persistent throughout their life.
Statement $(b)$ is correct: In Vertebrata,the notochord is present during the embryonic period and is replaced by a cartilaginous or bony vertebral column in the adult.
Statement $(c)$ is correct: Chordates possess a dorsal,hollow,and single central nervous system.
Statement $(d)$ is incorrect: The phylum Chordata is divided into three subphyla: Urochordata (or Tunicata),Cephalochordata,and Vertebrata. Hemichordata is a separate phylum.
Therefore,statements $(a)$,$(b)$,and $(c)$ are correct. Given the options,$(b)$ and $(c)$ are correct.

(B) The correct answer is option $B$ because the members of subphylum $Vertebrata$ possess a notochord during the embryonic period.
Since all vertebrates possess a notochord at some stage of their life,they are classified as chordates.
However,in adult vertebrates,the notochord is replaced by a cartilaginous or bony vertebral column.
In protochordates (urochordates and cephalochordates),a vertebral column is never formed. In urochordates,the notochord is present only in the larval tail,while in cephalochordates,it extends from head to tail region and persists throughout their life.
Therefore,because not all chordates develop a vertebral column,all chordates are not vertebrates.

(D) The classification of the mentioned animals is as follows:

Animals	Class	Phylum
Fishes	Pisces	Chordata
Amphibians	Amphibia	Chordata
Reptiles	Reptilia	Chordata
Birds	Aves	Chordata

As shown in the table,while these animals belong to different classes (Pisces,Amphibia,Reptilia,and Aves),they all share the same phylum,which is $Chordata$. Therefore,they are kept in the same phylum.

(D) All chordates share the following fundamental characteristics: they are bilaterally symmetrical,coelomates,triploblastic,and possess a closed circulatory system. They also exhibit an organ-system level of body organization.

(C) In a closed circulatory system,blood circulates through a series of blood vessels of varying diameters,$i.e.$,arteries,veins,and capillaries,without coming into direct contact with body cells.
Closed circulatory systems are characteristic of Annelids,cephalopod molluscs,and chordates.
Earthworms belong to the phylum $Annelida$,which possesses a closed circulatory system.
Cephalopod molluscs (such as squids and octopuses) are unique among molluscs for having a closed circulatory system.

(B) . Absence of notochord: This is a characteristic feature of non-chordates.
$B$. Heart is ventral: This is incorrect because in non-chordates, the heart (if present) is dorsal in position, whereas it is ventral in chordates.
$C$. Gill slits are absent: This is a characteristic feature of non-chordates.
$D$. Chitinous exoskeleton present: This is found in many non-chordates like arthropods.
Therefore, the statement "Heart is ventral" is not a characteristic of non-chordates.