Arthropoda, Mollusca and Echinodermata Practice Questions
40 free Arthropoda, Mollusca and Echinodermata practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following structures is a unique characteristic of the Phylum Echinodermata used for locomotion and food handling?
- A Segmented parapodia
- B Water vascular system
- C Chitinous radula
- D Articulated jointed appendages
Correct answer: Water vascular system
The water vascular system is a hydraulic network unique to echinoderms. It powers the tube feet (podia) through hydrostatic pressure, facilitating movement, adhesion, and food manipulation.
In Arthropods, the body cavity is greatly reduced and replaced by a blood-filled space known as the:
- A Pseudocoelom
- B Haemocoel cavity
- C Enterocoel
- D Spongocoel
Correct answer: Haemocoel cavity
Arthropods possess an open circulatory system where the true coelom is restricted to the reproductive and excretory organs. The primary body cavity is the haemocoel, through which haemolymph bathes the internal organs directly.
Which specialized rasping organ is found in the mouth of most Molluscs, except Bivalves?
- A Crystalline style
- B Radula (toothed ribbon)
- C Odontophore
- D Aristotle's lantern
Correct answer: Radula (toothed ribbon)
The radula is a chitinous, ribbon-like tongue equipped with rows of teeth. It is used to scrape or bore into food and is a hallmark of molluscan anatomy, though it is lost in filter-feeding bivalves.
Echinoderms exhibit a unique symmetry transition during their life cycle. Which of the following describes this correctly?
- A Asymmetrical larvae and bilateral adults
- B Bilateral larvae and radial adults
- C Radial larvae and bilateral adults
- D Spherical larvae and asymmetrical adults
Correct answer: Bilateral larvae and radial adults
Echinoderms are evolutionarily bilateral; their larvae show clear bilateral symmetry. During metamorphosis, they develop a secondary pentamerous radial symmetry that is characteristic of the adult body plan.
The respiratory organs in terrestrial arthropods like insects, consisting of a network of air-filled tubes, are called:
- A Book lungs
- B Gills
- C Tracheae
- D Ctenidia
Correct answer: Tracheae
Insects use a tracheal system — a network of air-filled tubes (tracheae) that branch into tiny tracheoles reaching every tissue. Air enters and exits through spiracles on the body wall, bypassing the need for a respiratory pigment in the blood.
Which class of Mollusca is characterized by a closed circulatory system and high intelligence?
- A Gastropoda
- B Bivalvia
- C Cephalopoda
- D Polyplacophora
Correct answer: Cephalopoda
Cephalopods (octopuses, squids, cuttlefish, nautiluses) are the most neurologically advanced molluscs. They are the only members of the phylum with a closed circulatory system, which supports the high oxygen demand of their active, predatory lifestyle and complex nervous systems.
The exoskeleton of Arthropods is primarily composed of which polysaccharide?
- A Cellulose
- B Glycogen
- C Chitin polymer
- D Pectin
Correct answer: Chitin polymer
Chitin, a nitrogen-containing polysaccharide, forms the structural basis of the arthropod cuticle. It is often embedded with proteins or calcium carbonate for rigidity. Because chitin does not grow, arthropods must periodically shed it through ecdysis (molting) to increase in size.
What is the function of 'Aristotle's Lantern' in sea urchins?
- A Light production for deep-sea dwelling
- B A complex chewing apparatus for grazing
- C A sensory organ for detecting chemicals
- D Excretion of metabolic wastes
Correct answer: A complex chewing apparatus for grazing
Aristotle's Lantern is a complex arrangement of five calcareous teeth and associated muscles. It functions as a chewing apparatus, allowing sea urchins to scrape algae from rocky surfaces and consume tough organic material.
Which structure in Molluscs is responsible for secreting the calcareous shell?
- A Muscular foot
- B Visceral mass
- C Mantle tissue
- D Ctenidium (gill)
Correct answer: Mantle tissue
The mantle is a specialized layer of tissue that drapes over the visceral mass and lines the inner surface of the shell. Its epithelial cells secrete calcium carbonate and conchiolin in layers, building and maintaining the protective shell in gastropods, bivalves, and cephalopods.
In the Phylum Arthropoda, the process of shedding the old exoskeleton is known as:
- A Metamorphosis
- B Ecdysis (molting)
- C Ameboid movement
- D Tagmatization
Correct answer: Ecdysis (molting)
Ecdysis (molting) is regulated by the steroid hormone ecdysone. The animal first secretes a new, soft cuticle beneath the old one, then splits the old exoskeleton and pulls free, allowing the new cuticle to expand and harden before rigidity is fully restored.
Which of the following is a characteristic excretory organ found in many Crustaceans?
- A Malpighian tubules (hindgut outgrowths)
- B Green glands
- C Statocysts
- D Nephridia
Correct answer: Green glands
Green glands (also called antennal glands) are located near the base of the antennae in crustaceans. They filter fluid from the haemocoel and excrete nitrogenous waste through pores, primarily assisting in osmoregulation.
Echinoderms possess a sieve-like plate that allows water to enter the water vascular system. This plate is called the:
- A Ampulla
- B Madreporite
- C Pedicellaria
- D Ossicle
Correct answer: Madreporite
The madreporite is a calcareous, sieve-like plate on the aboral surface of echinoderms. It acts as a pressure-equalizing valve and filters the intake of seawater into the stone canal, maintaining hydrostatic pressure within the water vascular system.
The fusion of segments into functional body regions, such as the cephalothorax in spiders, is known as:
- A Metamerism
- B Eutely (cell constancy)
- C Tagmatization
- D Segmentation
Correct answer: Tagmatization
Tagmatization is the evolutionary grouping of body segments into distinct functional units called tagmata (e.g., head, thorax, abdomen). This specialization allows different body regions to perform dedicated functions, improving locomotor and physiological efficiency.
Which class of Mollusca undergoes 'torsion' during larval development, rotating the visceral mass 180 degrees?
- A Bivalvia
- B Gastropoda
- C Scaphopoda
- D Cephalopoda
Correct answer: Gastropoda
Torsion is a developmental process unique to gastropod larvae, in which the entire visceral mass and mantle cavity rotate 180 degrees relative to the head and foot. This brings the mantle cavity, gills, and anus to an anterior position above the head, providing protection for these organs when the animal retracts into its shell.
The pincer-like structures on the surface of some echinoderms that keep the body free of debris and parasites are:
- A Tube feet
- B Spines
- C Pedicellariae
- D Dermal branchiae
Correct answer: Pedicellariae
Pedicellariae are minute, pincer-like appendages located on the body surface of sea stars and sea urchins. They snap shut to dislodge debris, remove parasites, and prevent encrusting organisms or settling larvae from colonizing the echinoderm's skin.
Which arthropod group is distinguished by having two pairs of antennae and biramous appendages?
- A Insecta
- B Arachnida
- C Crustacea
- D Myriapoda
Correct answer: Crustacea
Crustaceans are uniquely distinguished within Arthropoda by possessing two pairs of antennae (antennules and antennae). Their appendages are also typically biramous — each splitting into an inner endopodite and an outer exopodite — which is associated with aquatic locomotion and filter-feeding.
The 'Pearl' in oysters is formed by the deposition of nacreous layers around a foreign particle. Which part of the mollusc secretes these layers?
- A The outer edge of the foot
- B The mantle epithelium
- C The digestive gland
- D The gill filaments
Correct answer: The mantle epithelium
When a foreign particle lodges between the shell and the mantle, the mantle epithelial cells respond by secreting concentric layers of nacre (aragonite crystals bound by conchiolin) around the irritant. Over time, these layers accumulate to form a pearl.
What type of larva is common to many Molluscs and Annelids, suggesting an evolutionary link between the two phyla?
- A Planula larva
- B Triton larva
- C Trochophore
- D Bipinnaria
Correct answer: Trochophore
The trochophore is a free-swimming, ciliated larval stage bearing a characteristic band of cilia (the prototroch) used for locomotion and feeding. Its occurrence in both Mollusca and Annelida supports the grouping of these phyla within the Lophotrochozoa clade.
Spiders and scorpions belong to the subphylum Chelicerata. Which of the following do they LACK?
- A Cephalothorax
- B Antennae or antennules
- C Book lungs
- D Chelicerae
Correct answer: Antennae or antennules
Chelicerates (arachnids, horseshoe crabs, and sea spiders) are the only arthropod subphylum that lacks antennae entirely. Their first pair of appendages are the chelicerae — specialized pincers or fangs used in feeding and defense.
In Echinoderms, gas exchange often occurs through thin-walled protrusions of the coelom called:
- A Ctenidia (comb gills)
- B Dermal branchiae
- C Spiracles (air pores)
- D Tracheae (air tubes)
Correct answer: Dermal branchiae
Dermal branchiae, also called papulae, are thin-walled, finger-like extensions of the coelom that project through gaps between the calcareous ossicles. They increase surface area for the diffusion of oxygen and carbon dioxide between coelomic fluid and surrounding seawater.
Which of the following describes the respiratory pigment found in the hemolymph of many Molluscs and certain Arthropods, which turns blue when oxygenated?
- A Hemoglobin
- B Hemerythrin
- C Hemocyanin
- D Chlorocruorin
Correct answer: Hemocyanin
Hemocyanin is a copper-containing protein used for oxygen transport. Unlike iron-based hemoglobin, it is suspended directly in the plasma and gives the blood a distinct blue color when bound to oxygen.
In Echinoderms, the bulb-like structures that contract to force water into the tube feet, causing them to extend, are called:
- A Madreporites
- B Ampullae
- C Radial canals
- D Podia
Correct answer: Ampullae
The ampulla is a muscular sac located at the top of each tube foot. When it contracts, valves prevent water from backflowing into the radial canal, forcing the tube foot to extend via hydraulic pressure.
Which arthropod group is characterized by having four pairs of walking legs and a pair of pedipalps, but lacking antennae?
- A Crustacea
- B Hexapoda
- C Myriapoda
- D Chelicerata
Correct answer: Chelicerata
Chelicerates, including spiders, scorpions, and horseshoe crabs, are unique among arthropods for completely lacking antennae. They possess chelicerae for feeding and pedipalps for sensory or reproductive functions.
The 'Hepatopancreas' or digestive gland is a prominent organ for nutrient absorption and enzyme secretion in which two phyla?
- A Arthropoda and Mollusca
- B Mollusca and Echinodermata
- C Arthropoda and Echinodermata
- D Annelida and Mollusca
Correct answer: Arthropoda and Mollusca
Both Arthropods (especially crustaceans) and Molluscs possess a large, multifunctional organ often called the hepatopancreas that performs roles similar to the vertebrate liver and pancreas combined.
Which class of Mollusca is characterized by a shell divided into eight calcareous plates (valves) embedded in a tough girdle?
- A Gastropoda
- B Bivalvia
- C Monoplacophora
- D Polyplacophora
Correct answer: Polyplacophora
Polyplacophorans, commonly known as chitons, have a unique shell composed of eight overlapping plates. This allows them to curl into a ball for protection or adhere tightly to uneven rocky surfaces.
Insects excrete nitrogenous waste primarily in the form of uric acid through which specialized excretory structures?
- A Antennal green glands
- B Coxal glands
- C Flame cell protonephridia
- D Malpighian tubules
Correct answer: Malpighian tubules
Malpighian tubules are outgrowths of the digestive tract that remove wastes from the hemolymph. This system is highly efficient at conserving water, which is a key adaptation for terrestrial life.
What is the primary function of 'Tiedemann's bodies' found in the water vascular system of asteroids (sea stars)?
- A Production of amoebocytes
- B Regulating osmotic pressure
- C Light detection
- D Secreting digestive enzymes
Correct answer: Production of amoebocytes
Tiedemann's bodies are small glandular structures located on the ring canal of the water vascular system. They produce amoebocytes, phagocytic cells that circulate through the system and perform immune-like functions such as defense and waste removal.
Which of the following is a key difference between the circulatory systems of Arthropods and Cephalopod Molluscs?
- A Arthropods have an open system; Cephalopods have a closed system
- B Arthropods have a closed system; Cephalopods have an open system
- C Both have open systems with multiple hearts
- D Both have closed systems but use different pigments
Correct answer: Arthropods have an open system; Cephalopods have a closed system
Most molluscs and all arthropods have open circulatory systems where hemolymph bathes organs in a hemocoel. Cephalopods evolved a closed system with capillaries to support their high metabolic rates and active predatory lifestyle.
The 'Green Glands' (antennal glands) are the primary excretory organs in which group of animals?
- A Insects
- B Spiders
- C Centipedes
- D Crustacea
Correct answer: Crustacea
In many crustaceans, like crayfish and lobsters, the excretory organs are located at the base of the antennae. They filter fluid from the hemolymph and excrete dilute urine.
Which larval stage is unique to the Phylum Echinodermata, specifically seen in the class Asteroidea?
- A Bipinnaria
- B Veliger
- C Glochidium
- D Nauplius
Correct answer: Bipinnaria
The Bipinnaria is the first stage in the larval development of most sea stars. It is followed by the Brachiolaria stage before undergoing metamorphosis into the pentaradial adult.
The 'Crystalline Style' is a transparent, rod-like structure used to assist in the digestion of mucus-trapped food in which group?
- A Filter-feeding Bivalves
- B Predatory Gastropods
- C Carnivorous Cephalopods
- D Echinoids
Correct answer: Filter-feeding Bivalves
In Bivalves, the crystalline style rotates within a sac, pulling a 'mucus string' of food into the stomach while releasing digestive enzymes as it slowly dissolves at its tip.
Spiders utilize 'Book Lungs' for respiration. These structures are characterized by:
- A Internalized, leaf-like plates for gas exchange with hemolymph
- B Air-filled tubes branching throughout the body
- C External gills protected by an operculum
- D Thin protrusions of the body wall used for cutaneous respiration
Correct answer: Internalized, leaf-like plates for gas exchange with hemolymph
Book lungs consist of many thin, highly vascularized tissue layers (lamellae) arranged like pages in a book. This arrangement provides a large surface area for gas exchange between air and the spider's hemolymph.
Which class of Echinodermata lacks a mouth-down orientation and instead uses its tube feet primarily for filter feeding in a mouth-up position?
- A Holothuroidea
- B Ophiuroidea
- C Echinoidea
- D Crinoidea
Correct answer: Crinoidea
Crinoids (sea lilies and feather stars) are the most primitive living echinoderms. They sit or attach with their oral surface facing upward, using their branched arms and tube feet to capture plankton.
The 'Ommatidia' are the functional units of which arthropod organ?
- A Compound eye
- B Statocyst
- C Johnston's organ
- D Tympanum
Correct answer: Compound eye
Compound eyes are made of hundreds or thousands of individual ommatidia. Each ommatidium captures a small part of the visual field, allowing the arthropod to detect motion with great sensitivity.
Which of the following is a distinctive feature of the Class Holothuroidea (sea cucumbers)?
- A A rigid endoskeleton of fused plates
- B Reduction of ossicles to microscopic spicules within a leathery skin
- C A large, well-developed Aristotle's lantern
- D The presence of eight sucker-tipped arms used for crawling and feeding
Correct answer: Reduction of ossicles to microscopic spicules within a leathery skin
Sea cucumbers have a soft, elongated body. Their endoskeleton is not a solid test but is reduced to tiny, isolated calcareous ossicles (spicules) embedded in the muscular body wall.
What is the function of the 'Osphradium' in aquatic molluscs?
- A Balancing and orientation
- B Chemoreceptor used to 'taste' the incoming water
- C Secreting the protective periostracum layer of the shell
- D Pumping blood into the mantle cavity
Correct answer: Chemoreceptor used to 'taste' the incoming water
The osphradium is a sensory organ located near the gills. It monitors the chemical composition of water and detects silt levels, helping the mollusc assess the environment for food or toxins.
Which group of arthropods is characterized by having one pair of legs per body segment and a pair of venomous maxillipeds (forcipules)?
- A Diplopoda (Millipedes)
- B Chilopoda (Centipedes)
- C Isopoda
- D Arachnida
Correct answer: Chilopoda (Centipedes)
Centipedes (Chilopoda) are predatory and possess one pair of legs per segment. Their first pair of appendages is modified into venomous claws used to paralyze prey.
In Bivalves, the 'Glochidium' larva is specialized for:
- A Long-distance swimming freely through the open ocean waters
- B Parasitizing the gills or fins of fish for dispersal
- C Burrowing into soft mud immediately after hatching
- D Developing into a terrestrial slug
Correct answer: Parasitizing the gills or fins of fish for dispersal
Glochidia are the larvae of many freshwater mussels. They attach to fish hosts as temporary parasites, allowing the sedentary mussels to disperse upstream and colonize new habitats.
Which mechanism do Brittle Stars (Ophiuroidea) primarily use for locomotion, distinguishing them from Sea Stars?
- A Slow, gradual gliding across surfaces using suction-tipped tube feet
- B Rapid rowing or thrashing of their flexible, snake-like arms
- C Rolling across the seafloor using spines
- D Jet propulsion by expelling water from the bursae
Correct answer: Rapid rowing or thrashing of their flexible, snake-like arms
Ophiuroids have distinct central disks and highly flexible arms. Unlike sea stars, their tube feet lack suckers and are used for sensing and feeding; locomotion is achieved by muscular arm movements.
The 'Cuvierian tubules' are defensive structures found in some members of which group?
- A Cephalopods
- B Crustaceans
- C Sea cucumbers
- D Some sea urchins
Correct answer: Sea cucumbers
Some sea cucumbers, when threatened, can expel sticky, toxic Cuvierian tubules from their anus. These entangle and distract predators, sometimes even eviscerating their internal organs as a more extreme defense.