NEET Animal Kingdom Previous Year Questions with Solutions

In animal morphology, when any longitudinal plane passing through the central body axis divides an organism into two identical mirrored halves, the body plan exhibits radial symmetry. Examples include coelenterates, ctenophores, and adult echinoderms.

• • Statement I is verbatim text from NCERT Animal Kingdom (Section 4.1.2 Symmetry).

Echinoderms display a unique developmental transition in symmetry: they develop from free-swimming ciliated larvae that are bilaterally symmetrical (reflecting their deuterostome ancestry with chordates), which then metamorphose into adults exhibiting pentamerous radial symmetry.

• • Because larvae are bilateral, stating that "both adults and larvae are radially symmetrical" is definitively false.

Since Statement I is correct and Statement II is incorrect, Option (3) is the solely valid choice.

• • Matches official NTA final answer key Option C / (3).

The class name Reptilia is derived from the Latin verb "repere" or "reptum", which signifies "to creep or crawl". This refers directly to their terrestrial creeping or crawling mode of locomotion.

• • Matches NCERT opening sentence for Class Reptilia.

In most reptiles (lizards, snakes, turtles), the heart is 3-chambered, possessing two atria and an incompletely divided single ventricle. However, order Crocodilia (crocodiles, alligators, gharials) possesses a fully partitioned, complete 4-chambered heart (two atria and two ventricles). Therefore, the absolute assertion that "ALL organisms belonging to Reptilia have three chambered heart" is false.

• • The universal qualifier "All" invalidates Statement II.

Statement I is correct and Statement II is incorrect. Option (3) is the solely accurate selection.

• • Matches official NTA final answer key Option C / (3).

Animals belonging to phylum Chordata are fundamentally characterized by four structural features present at some stage during their ontogeny (embryonic or adult life): (1) A solid, unsegmented dorsal notochord, (2) A dorsal hollow nerve cord, (3) Paired pharyngeal gill slits, and (4) A post-anal tail.

• • In terrestrial amniotes, pharyngeal pouches form in embryos and give rise to structures like Eustachian tubes.

Table 4.1 in NCERT directly compares chordates and non-chordates: In chordates, "Pharyngeal gill slits are present", whereas in non-chordates, "Gill slits are absent".

• • Stating "Absence of gills" contradicts chordate taxonomy.

Option (1) Presence of notochord (True chordate trait). Option (2) Central nervous system is dorsal (True chordate trait). Option (3) Absence of gills (NOT a chordate trait; chordates have pharyngeal gill slits). Option (4) Presence of post-anal tail (True chordate trait).

• • Matches official NTA final answer key Option C / (3).

The body cavity between the body wall and the gut wall is a fundamental criterion for animal classification:

• • Coelomates (Eucoelomates): Possess a true coelom completely lined by mesodermal epithelium (peritoneum). Somatic mesoderm lines the inner body wall, and splanchnic mesoderm surrounds the alimentary canal. Examples: Annelids, Arthropods, Molluscs, Echinoderms, Hemichordates, Chordates.
• • Acoelomates: Lack any body cavity; space between gut and body wall is filled with mesodermal parenchyma tissue. Example: Platyhelminthes.
• • Pseudocoelomates: The body cavity is not completely lined by mesoderm. Instead, mesoderm is present only towards the body wall (or as scattered pouches between ectoderm and endoderm), and the endodermal alimentary canal has no surrounding mesodermal tissue. Example: Aschelminthes (roundworms).

The researcher observes: mesoderm towards the body wall, but NO mesodermal tissue towards the alimentary canal. This precisely describes a false coelom or pseudocoelom, which persists from the embryonic blastocoel without developing a visceral peritoneum around the gut.

The coelome of this newly found animal is a pseudocoel, and the organism is classified as a Pseudocoelomate.

Cyclostomes belong to Subphylum Vertebrata, Division Agnatha (animals lacking jaws):

• • They represent the only surviving jawless vertebrates.
• • Living representatives include lampreys (*Petromyzon*) and hagfishes (*Myxine*).

Morphological specializations for their lifestyle:

• • NCERT states unequivocally: "All living members of the class Cyclostomata are ectoparasites on some fishes."
• • They possess a ventral, circular, jawless mouth modified into a powerful suctorial disc equipped with horny epidermal teeth.
• • They attach to the lateral body surfaces of larger teleost fishes, rasps their flesh, and suck their blood and body fluids as obligate ectoparasites.

All living cyclostomes are categorized ecologically and physiologically as Ectoparasites.

Phylum Chordata is defined by three diagnostic morphological features present at some stage of life: a dorsal hollow nerve cord, a notochord, and paired pharyngeal gill slits:

• • Phylum Chordata is divided into three subphyla: Urochordata (Tunicata), Cephalochordata, and Vertebrata.
• • Urochordata and Cephalochordata are collectively called protochordates (invertebrate chordates). In Urochordata, notochord is present only in the larval tail; in Cephalochordata, notochord extends from head to tail and persists throughout life.
• • In protochordates, a vertebral column is never formed. Hence, they are chordates, but NOT vertebrates.

Vertebrates represent a derived clade within Chordata:

• • Members of subphylum Vertebrata possess a notochord during the embryonic period.
• • In adults, this embryonic notochord is replaced by a protective cartilaginous or bony vertebral column (backbone).
• • Because all vertebrates inherit the ancestral chordate traits in the embryo, all vertebrates are chordates.
• • Because protochordates lack a vertebral column, all chordates are not vertebrates.

Both statements are true and Reason (R) provides the definitive structural and evolutionary explanation for Assertion (A).

Echinoderms possess a coelomic hydraulic circulatory network termed the water vascular or ambulacral system:

• • Water enters through a perforated calcareous plate called the madreporite, passes through the stone canal into the ring canal, and travels through radial canals to reach muscular ampullae and tube feet (podia).
• • Hydraulic hydrostatic pressure changes in the tube feet power their coordinated biological functions.

The precise functional roles of the water vascular system:

• • Locomotion: Tube feet adhere to substrata via suction and contraction, propelling the animal forward.
• • Capture and transport of food: Tube feet and ambulacral grooves pry open bivalve prey and convey food particles to the ventral mouth.
• • Respiration: Thin, exposed epithelial surfaces of tube feet and dermal branchiae (papulae) facilitate gas exchange between coelomic fluid and seawater.
• • Hence, statements A (Respiration and Locomotion) and C (Capture and transport of food) are completely CORRECT.

Differentiating physiological systems in Echinodermata:

• • Excretory system: NCERT explicitly emphasizes that an specialized excretory system is completely absent in echinoderms; nitrogenous waste (ammonia) diffuses directly through thin body walls and dermal gills. Thus, any statement including excretion (B and E) is incorrect.
• • Digestive system: Digestion is accomplished by the complete digestive tract (ventral mouth, stomach, pyloric caeca, and dorsal anus), not the water vascular system. Thus, statements D and E are incorrect.

Only Statements A and C are true functions of the water vascular system, corresponding to Option (2).

Myxine is a jawless marine cyclostome commonly known as the hagfish (B -> I). Pristis possesses a prolonged snout with lateral teeth, belonging to Chondrichthyes, commonly known as sawfish (C -> II).

Exocoetus is a marine bony fish with large pectoral fins, commonly called the flying fish (D -> IV). Pterophyllum is a popular freshwater ornamental aquarium fish known as angel fish (A -> III).

A-III, B-I, C-II, D-IV matches Option (4).

Pleurobrachia and Ctenoplana are prominent model organisms representing phylum Ctenophora (A -> II). The mouth of molluscs contains a file-like rasping organ for feeding, called radula (B -> I).

Hemichordates have a rudimentary structure in the collar region called stomochord, a structure similar to notochord (C -> IV). In class Osteichthyes (bony fishes), air bladder is present which regulates buoyancy, preventing them from sinking (D -> III).

A-II, B-I, C-IV, D-III corresponds to Option (4).

Presence or absence of a cavity between the body wall and the gut wall is very important in classification. The body cavity, which is lined by mesoderm is called coelom. Animals possessing coelom are called coelomates, e.g., annelids, molluscs, arthropods, echinoderms, hemichordates and chordates. Statement A is correct.

In some animals, 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 pseudocoelom and the animals possessing them are called pseudocoelomates, e.g., Aschelminthes (Statement C is false). The animals in which the body cavity is absent are called acoelomates, e.g., Platyhelminthes (Statement D is false). Sponges (Porifera) lack true body cavities altogether (Statement B is false).

Only statement A is correct, corresponding to Option (4).

1. Notochord: Present in chordates; Absent in non-chordates (Statement B is TRUE). 2. Central Nervous System: In chordates, it is dorsal, hollow, and single. In non-chordates, it is ventral, solid, and double (Statement C is FALSE for non-chordates). 3. Pharyngeal Gill Slits: Present in chordates; Absent in non-chordates (Statement A is FALSE for non-chordates). 4. Heart: Ventral in chordates; Dorsal (if present) in non-chordates (Statement D is TRUE). 5. Post-anal Tail: Present in chordates; Absent in non-chordates (Statement E is TRUE).

Statements B, D, and E accurately characterize non-chordates.

B, D & E only corresponds to Option (1).

Correlating each taxon with its respective excretory or osmoregulatory adaptation:

NCERT Structural Organisation in Animals states under Cockroach Excretion: "In addition, the fat body, nephrocytes and urecose glands also help in excretion."

Matching A-III immediately isolates Option (4) uniquely, since all other options incorrectly match A with I or II.

Symmetry is a primary foundational architectural feature used to classify animals into major branches:

NCERT states under Symmetry: "Coelenterates, ctenophores and echinoderms have this kind of body plan (radial symmetry). Annelids, arthropods, etc., where the body can be divided into identical left and right halves in only one plane, exhibit bilateral symmetry." Under Hemichordata, NCERT specifies: "They are bilaterally symmetrical, triploblastic and coelomate animals."

Because Hemichordata exhibits bilateral symmetry throughout its entire life history, radial symmetry is never found in adults of this phylum.

Animals belonging to phylum Chordata are characterized by four defining morphological features present at some stage in their life history:

Comparing internal organ orientations against non-chordates:

In Table 4.1 "Comparison of Chordates and Non-chordates", NCERT states: - "Central nervous system is dorsal, hollow and single." (Statement A is FALSE) - "Pharynx perforated by gill slits." (Statement C is TRUE) - "Heart is ventral." (Statement D is FALSE) - Chordates are true coelomates, while pseudocoelom is restricted to Aschelminthes (Statement E is FALSE).

Class Mammalia possesses anatomical hallmarks that are uniquely derived and not shared with other vertebrate classes:

Analyzing the errors in distractor options: - Mammals possess a dicondylic skull with two occipital condyles (monocondylic skulls characterize reptiles and birds). - Tympanic membrane represents the ear in amphibians and reptiles as well; it is not unique to mammals. - Mammals exhibit direct development without intermediate metamorphic larval stages.

NCERT states verbatim under Class Mammalia: "The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which the young ones are nourished... The skin of mammals is unique in possessing hair. External ears or pinnae are present."

Each invertebrate phylum possesses defining anatomical synapomorphies: - (a) Metamerism: True internal and external segmented body organization with serial repetition of organs, characteristic of Annelida (e.g., earthworm, Nereis). - (b) Canal system: Sponges possess a water transport or canal system where water enters through microscopic pores (*ostia*) into a central cavity (*spongocoel*), driven by flagellated choanocytes, exiting via the *osculum*; diagnostic of Porifera. - (c) Comb plates: Ctenophores (comb jellies/sea walnuts) bear eight external rows of ciliated comb plates that function exclusively in locomotion; diagnostic of Ctenophora. - (d) Cnidoblasts (cnidocytes): Specialized defensive and prey-capturing cells containing stinging capsules (*nematocysts*); characteristic of Coelenterata / Cnidaria.

Comparing the mapped matrix with the given choices confirms: (a) $\rightarrow$ (iii) (b) $\rightarrow$ (iv) (c) $\rightarrow$ (ii) (d) $\rightarrow$ (i) This perfectly corresponds to Option (3).

Birds (Class Aves) exhibit numerous anatomical specializations designed to minimize weight during flight: - The endoskeleton is fully ossified (bony). - The long bones are hollow and contain air cavities (pneumatic bones) connected to auxiliary respiratory air sacs. - This skeletal adaptation significantly reduces specific gravity while maintaining structural tensile strength under aerodynamic loading. - Pneumatic bones are unique to Class Aves among extant vertebrate classes.

- (1) *Neophron* (Vulture): A true avian genus belonging to Class Aves. Possesses pneumatic bones. - (2) *Hemidactylus* (Wall lizard): Class Reptilia. Possesses solid, non-pneumatic bones. - (3) *Macropus* (Kangaroo): Class Mammalia (metatherian marsupial). Possesses heavy, marrow-filled non-pneumatic bones adapted for saltatory bipedal locomotion. - (4) *Ornithorhynchus* (Platypus): Class Mammalia (prototherian monotreme). Possesses dense solid bones.

Each genus listed is a classic NCERT type specimen representing distinct invertebrate phyla: - (a) *Physalia* (Phylum Coelenterata / Cnidaria): Colonial siphonophore possessing gas-filled pneumatophore float resembling an 18th-century warship, commonly called Portuguese Man of War. - (b) *Limulus* (Phylum Arthropoda): Commonly known as the King crab or horseshoe crab. Having remained virtually unchanged over hundreds of millions of years, it is universally designated a Living fossil. - (c) *Ancylostoma* (Phylum Aschelminthes): Intestinal nematode parasite commonly named the Hookworm. - (d) *Pinctada* (Phylum Mollusca): Bivalve mollusc commercially cultured for natural and cultured nacre pearls, commonly termed the Pearl oyster.

Matching sequence: (a) -> (ii), (b) -> (iii), (c) -> (iv), (d) -> (i). This corresponds uniquely and unambiguously to Option (3).

- (a) Metagenesis in Helminths (FALSE): Metagenesis is the alternation of asexual polyp generation with sexual medusa generation, characteristic of Cnidarians (*Obelia*). Helminths exhibit complex parasitic life cycles with multiple larval stages, but never metagenesis. - (b) Echinoderm Germ Layers and Coelom (TRUE): Adult echinoderms possess triploblastic germ layer organization (ectoderm, mesoderm, endoderm) and a true enterocoelic coelom lined by mesoderm. - (c) Body Organization of Roundworms (TRUE): Aschelminthes (roundworms) represent the first phylum in evolutionary phylogeny to attain the organ-system level of body organization along with a pseudocoelom and a complete alimentary canal with muscular pharynx. - (d) Function of Ctenophore Comb Plates (FALSE): Ctenophores (comb jellies or sea walnuts) possess eight external rows of ciliated comb plates which function exclusively in locomotion, not digestion. Digestion in ctenophores is both extracellular and intracellular. - (e) Water Vascular System in Echinodermata (TRUE): The water vascular (ambulacral) system is the unique diagnostic anatomical hallmark of phylum Echinodermata, driving locomotion, capture/transport of food, and respiration via tube feet (podia).

Only statements (b), (c), and (e) are correct. Combining them leads unequivocally to Option (4).

- (a) Gregarious, polyphagous pest: _Locusta_ (Locust, Phylum Arthropoda, Class Insecta) is an economically devastating swarming insect pest that destroys agricultural crops en masse. - (b) Larva bilateral and adult radial symmetry: Characteristic developmental hallmark of Phylum Echinodermata (_Asterias_, starfish). Free-swimming bipinnaria/dipleurula larvae exhibit primary bilateral symmetry, while adults metamorphose into pentamerous radial symmetry. - (c) Book lungs: Respiratory organs found in terrestrial arachnids such as _Scorpion_ and spiders (Phylum Arthropoda). - (d) Bioluminescence: The emission of light by a living organism, exquisitely manifested in Phylum Ctenophora (_Ctenoplana_ and _Pleurobrachia_).

Matching sequence is: (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii). This corresponds uniquely to Option (2).

Phylum Chordata is defined by four canonical features present at some stage of ontogeny: 1. Notochord. 2. Dorsal hollow nerve cord (Statement (c) is True; contrasts with ventral solid cord in non-chordates). 3. Pharyngeal gill slits. 4. Post-anal tail.

Phylum Chordata is divided into three subphyla: - 1. Subphylum Urochordata (Tunicata): Notochord is present strictly in the tail of the free-swimming larva (retrogressive metamorphosis causes loss in sessile adults, e.g. *Ascidia*, *Salpa*). Statement (a) falsely describes Cephalochordata (*Branchiostoma*). - 2. Subphylum Cephalochordata: Notochord extends from head to tail (rostrum to caudal tip) and persists throughout life. - 3. Subphylum Vertebrata: The notochord is present during the embryonic period only; it is subsequently replaced by a cartilaginous or bony vertebral column in the adult (Statement (b) is True: "All vertebrates are chordates, but all chordates are not vertebrates"). - Status of Hemichordata: Historically classified as a subphylum of Chordata, Hemichordata is now classified as an independent non-chordate phylum because the stomochord is not a true notochord (making statement (d) false).

Class Cyclostomata includes jawless living vertebrates (e.g., Petromyzon, Myxine) that possess an elongated body bearing 6 to 15 pairs of gill slits for respiration. Thus, (a) matches (ii).

Class Chondrichthyes (cartilaginous fishes like Scoliodon) possess an asymmetrical heterocercal caudal fin where the vertebral column extends into the larger dorsal lobe. Thus, (b) matches (iii).

Class Osteichthyes (bony fishes like Exocoetus, Labeo, Betta) possess an air bladder (swim bladder) which regulates buoyancy, preventing them from sinking. Thus, (c) matches (iv).

Trygon (sting ray) is a cartilaginous fish that possesses a venomous serrated spine (poison sting) on its whip-like tail for defense. Thus, (d) matches (i).

Animals in which the body cavity is absent and the mesoderm forms a solid packing tissue (parenchyma) between the ectoderm and gut wall are called acoelomates.

In bilateral symmetry, the body can be divided into identical left and right halves in only one plane.

- Platyhelminthes (Flatworms): Triploblastic, bilaterally symmetrical, and acoelomate (NCERT verbatim: "acoelomates, e.g., Platyhelminthes"). - Aschelminthes: Bilaterally symmetrical, but PSEUDOCOELOMATE. - Annelida: Bilaterally symmetrical, but TRUE COELOMATE (schizocoelomate). - Ctenophora: Radially symmetrical and diploblastic.

Platyhelminthes uniquely satisfies both conditions of being bilaterally symmetrical and acoelomate.