Animal Kingdom — Set 4

Correct Answer: C. Book lungs

• **Book lungs** = folded lamellar organs found in arachnids like scorpions and spiders that allow direct oxygen diffusion between air pockets and circulating hemolymph. • **Named after books** — the parallel thin lamellae (leaf-like plates) stacked together resemble the pages of a book, massively increasing gas-exchange surface area. • Found in the abdomen; blood flows between lamellae while air enters through a slit called the spiracle on the body surface. • 💡 Option A (Gills) is wrong because gills are aquatic organs that extract dissolved oxygen from water, not air; Option B (Skin) is wrong because cutaneous respiration is only a minor supplement in a few arachnids, not the primary organ; Option D (Tracheae) is wrong because tracheae are the primary respiratory tubes of insects (Hexapoda), not arachnids.

Correct Answer: D. Physalia

• **Physalia** = a siphonophore cnidarian that drifts on the ocean surface using a gas-filled pneumatophore (float bladder), with trailing venomous tentacles that can extend up to 30 metres. • **Colonial superorganism** — Physalia is not a single animal but a colony of genetically identical zooids, each specialised for one function: feeding, defence, reproduction, or flotation. • Its sting injects a powerful neurotoxin causing intense pain, cardiac effects, and occasionally death in humans. • 💡 Option A (Aurelia) is wrong because Aurelia is the common moon jellyfish, a true medusoid solitary cnidarian; Option B (Meandrina) is wrong because Meandrina is a stony brain coral, a reef-building anthozoan; Option C (Adamsia) is wrong because Adamsia is a sea anemone that lives commensally on hermit crab shells.

Correct Answer: B. Shedding of exoskeleton

• **Ecdysis** = the periodic moulting or shedding of the rigid chitinous exoskeleton in arthropods (and cuticle in nematodes), allowing the soft-bodied animal to grow before the new exoskeleton hardens. • **Hormonal trigger** — in insects, the hormone ecdysone (a steroid) initiates ecdysis; the animal is highly vulnerable to predation during the brief soft-body period between moults. • Animals that undergo ecdysis are grouped in the superphylum Ecdysozoa, which includes arthropods and nematodes. • 💡 Option A (Feeding) is wrong because feeding is called ingestion or predation, entirely unrelated to exoskeleton shedding; Option C (Reproduction) is wrong because reproductive processes involve gametogenesis, fertilisation, or budding, not cuticle replacement; Option D (Digestion) is wrong because digestion refers to enzymatic breakdown of food in the gut.

Correct Answer: B. Platyhelminthes

• **Platyhelminthes** = the phylum of acoelomate, bilaterally symmetrical worms whose body is dorsoventrally flattened — Greek 'platys' (flat) + 'helminthos' (worm) — including tapeworms, flukes, and planarians. • **No body cavity** — being acoelomate (no true coelom), nutrients and gases diffuse directly through the flat body; they have no circulatory or respiratory system. • Medical significance: Taenia (tapeworm) and Fasciola (liver fluke), both platyhelminthes, are major human and livestock parasites. • 💡 Option A (Coelenterata) is wrong because coelenterates like jellyfish are radially symmetrical diploblastic animals with a gastrovascular cavity; Option C (Aschelminthes) is wrong because Aschelminthes are roundworms with a pseudocoelomate cylindrical body, not flattened; Option D (Annelida) is wrong because annelids are segmented worms (earthworm, leech) with a true coelom.

Correct Answer: D. Two

• **Two-chambered heart** = fish possess a single atrium (receives deoxygenated blood from body) and a single ventricle (pumps it to the gills), forming a single-circuit or single-loop circulatory system. • **Single circulation** — blood passes through the heart only once per complete circuit: body → heart → gills (for oxygenation) → body tissues; this is less efficient than double circulation. • The sinus venosus and conus arteriosus are accessory chambers that assist flow but are not true pumping chambers. • 💡 Option A (Three) is wrong because a three-chambered heart (two atria + one ventricle) is found in amphibians and most reptiles, enabling partial separation of oxygenated and deoxygenated blood; Option B (Four) is wrong because a four-chambered heart with complete separation is the hallmark of birds and mammals; Option C (One) is wrong because no vertebrate has only one true heart chamber.

Correct Answer: B. Bat

• **Bat** = a member of Order Chiroptera and the only flying mammal; like all mammals it is endothermic (warm-blooded), maintaining a stable core body temperature of ~37 °C through internal metabolic heat production regardless of ambient temperature. • **High metabolic rate** — bats have one of the fastest metabolic rates among mammals, essential for powered flight, echolocation, and activity in cool nocturnal environments. • Bats are also unique among small mammals for extreme longevity relative to their body size, partly linked to their endothermic regulation. • 💡 Option A (Snake) is wrong because snakes are ectothermic reptiles that rely on external heat sources (sun-basking) to regulate body temperature; Option C (Frog) is wrong because frogs are ectothermic amphibians whose body temperature fluctuates with the environment; Option D (Shark) is wrong because most sharks are ectothermic fish, though a few (e.g., Great White) are partially endothermic regionally.

Correct Answer: B. Porifera

• **Porifera** = the phylum of sponges, the most primitive multicellular animals (Metazoa); their bodies are perforated by a network of pores (ostia), canals, and chambers through which water circulates for filter-feeding and gas exchange. • **Unique cell type** — choanocytes (collar cells) line the interior canals and use flagella to drive water flow while trapping food particles; this cell type is not found in any other animal phylum. • Sponges lack true tissues, organs, and symmetry; they have no nervous, digestive, or circulatory systems, relying entirely on the water canal system. • 💡 Option A (Cnidaria) is wrong because cnidarians (jellyfish, corals, hydra) are diploblastic animals with radial symmetry and specialised stinging cells called cnidocytes; Option C (Echinodermata) is wrong because echinoderms (starfish, sea urchins) are triploblastic, have a water vascular system, and show pentaradial symmetry; Option D (Mollusca) is wrong because molluscs (snails, clams, octopus) have a distinct body plan with a mantle, foot, and often a shell.

Correct Answer: B. Reptilia

• **Reptilia** = cold-blooded (ectothermic) vertebrates characterised by a dry, keratinised scaly skin that prevents desiccation and by amniotic eggs with a tough, leathery shell — adaptations that freed them from water for reproduction. • **Amniotic egg advantage** — the leathery shell, along with internal membranes (amnion, chorion, allantois), allows embryonic development on dry land without the egg drying out, a key evolutionary advance over amphibians. • Crocodilians are the exception: they have a four-chambered heart (like birds and mammals) even though they belong to Reptilia. • 💡 Option A (Mammalia) is wrong because mammals have hair/fur and mammary glands; most give birth to live young (viviparous) and do not lay eggs (except monotremes like platypus); Option C (Aves) is wrong because birds lay hard, calcified eggs (not leathery) and have feathers instead of scales; Option D (Amphibia) is wrong because amphibians lay soft, gelatinous eggs in water and have moist, glandular skin lacking scales.

Correct Answer: A. Excretion

• **Malpighian tubules** = slender blind-ended tubules that open into the insect hindgut; they actively absorb nitrogenous wastes (mainly uric acid) and ions from the surrounding hemolymph and pass them into the gut for elimination — serving as the kidney equivalent in insects. • **Water conservation** — insects excrete uric acid (insoluble, semi-solid) rather than urea or ammonia, so virtually no water is lost in excretion; this is critical for survival in arid terrestrial environments. • Named after Italian biologist Marcello Malpighi (17th century); also found in spiders and other arachnids. • 💡 Option B (Digestion) is wrong because digestion occurs in the midgut (mesenteron) where digestive enzymes break down food; Option C (Respiration) is wrong because insects breathe via a tracheal system — branching air tubes that carry oxygen directly to tissues; Option D (Circulation) is wrong because insects have an open circulatory system with hemolymph circulated by a dorsal tubular heart, entirely separate from excretion.

Correct Answer: A. Kiwi

• **Kiwi** = a small, nocturnal, flightless ratite bird belonging to genus Apteryx, endemic (found only in) New Zealand, and the country's national symbol; it is the only bird with nostrils at the tip of its long beak, used to probe soil for earthworms and insects. • **Unique adaptations** — kiwis have vestigial, hidden wings with no flight muscles, hair-like feathers unlike the vaned feathers of flying birds, and a highly developed sense of smell — extremely rare among birds. • The kiwi lays the largest egg relative to body size of any bird: the egg can be up to 20% of the female's body weight. • 💡 Option B (Penguin) is wrong because penguins are flightless birds native to the Antarctic and Southern Ocean regions, not New Zealand (though some species visit NZ coasts); Option C (Ostrich) is wrong because the ostrich is the world's largest flightless bird, native to Africa; Option D (Rhea) is wrong because rheas are large flightless birds native to South America.