Q.Write three specific characteristics of phylum arthropoda.
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Phylum Arthropoda – The Jointed-Legged Majority
Think about the most successful design for an animal on land, in water, and in the air. What would it need? A tough outer suit of armour for protection, flexible joints so you can still move, and a body plan that can be adapted for crawling, flying, swimming, or even parasitism. That is exactly what arthropods have perfected.
Arthropods are the largest phylum in the animal kingdom. Over two-thirds of all named animal species on Earth are arthropods. You have met them constantly: cockroaches in the kitchen, butterflies in the garden, crabs at the beach, spiders in the corner, and scorpions in the desert. What unites them is a shared blueprint.
The Core Idea: Jointed Legs and an External Skeleton
The name itself gives it away: arthro means jointed, poda means foot or leg. Every arthropod has paired, jointed appendages. But the real game-changer is the exoskeleton — a hard, non-living outer covering made of a tough polysaccharide called chitin.
This exoskeleton is not a soft skin. It is a rigid suit of armour that provides support, protects internal organs, and prevents water loss (critical for life on land). The catch? It does not grow with the animal. So arthropods must periodically shed it — a process called moulting or ecdysis — and grow a new, larger one.
Do not confuse the exoskeleton with a shell. A snail's shell is a single piece; an arthropod's exoskeleton is a segmented, jointed suit. The joints are thin, flexible membranes of chitin that allow movement where the armour would otherwise lock up.
The Body Plan: Segments with a Purpose
Arthropod bodies are segmented (metameric), but unlike earthworms where each segment looks the same, arthropod segments are grouped into specialised regions called tagmata. The most common arrangement is three tagmata:
- Head – Sensory and feeding centre. Bears eyes, antennae, and mouthparts.
- Thorax – Locomotion centre. Bears legs and, in many, wings.
- Abdomen – Visceral centre. Contains digestive, reproductive, and excretory organs.
Not all arthropods follow this exactly. Spiders have a cephalothorax (head + thorax fused) and an abdomen. Centipedes have a head and a long trunk of many similar segments. But the principle of tagmatisation — grouping segments for specialised functions — is universal.
Internal Systems: Open Circulation and Beyond
Arthropods have a complete digestive system (mouth to anus) with specialised regions. But their circulatory system is open: blood (called haemolymph) is pumped by a tubular heart into body spaces (sinuses) and bathes the organs directly. There are no fine capillaries.
Respiration varies by habitat:
- Aquatic arthropods (crabs, prawns) use gills.
- Terrestrial arthropods (insects) use a network of air tubes called tracheae.
- Some (spiders, scorpions) use book lungs.
Excretion is handled by structures like Malpighian tubules (in insects) or green glands (in crustaceans). The nervous system is a ventral nerve cord with ganglia, and sense organs are highly developed — compound eyes, antennae for touch and smell, and statocysts for balance.
The key diagnostic features of Phylum Arthropoda are:
- Jointed appendages (legs, antennae, mouthparts)
- Chitinous exoskeleton that is moulted periodically
- Segmented body organised into tagmata
- Open circulatory system with a dorsal heart
- Ventral nerve cord with paired ganglia
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Three defining features of phylum Arthropoda: jointed appendages (the phylum's name literally means "jointed feet"), a hard chitinous exoskeleton, and a segmented body organised into distinct regions (e.g., head, thorax, abdomen). …
Arthropoda is the largest animal phylum, and its members are unified by a hard external skeleton made of chitin, limbs divided into movable joints, and a body plan built from repeated, often specialised segments.
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Jointed appendages: the name Arthropoda comes from Greek "arthron" (joint) + "podos" (foot) — every member has paired, jointed appendages (legs, antennae, mouthparts) that allow precise, flexible movement despite the rigid exoskeleton, since movement happens at the joints between hardened segments.
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Chitinous exoskeleton: the body is covered by a hard, non-living cuticle made largely of chitin, which provides protection and a surface for muscle attachment, but must be periodically shed (moulting/ecdysis) to allow growth, since it cannot expand once hardened.
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- CBSE 2026Set ANNUAL1 markMCQQ.The type of vision in Cockroach is :(a) Mosaic(b) Three-dimensional(c) Cockroaches do not have vision(d) Two-dimensional
›Reveal solutionSolution
Cockroaches see through compound eyes built of many ommatidia, and the combined partial images from each ommatidium form a mosaic picture of the surroundings.
A cockroach's compound eye is composed of a large number of tightly packed visual units called ommatidia, each with its own lens, crystalline cone, and set of light-sensitive (photoreceptor) cells. Each ommatidium samples light from a very narrow angle of the visual field and sends its own small, separate image fragment to the brain. The brain assembles all these tiny fragments together, much like tiles in a mosaic, into one composite picture of the surroundings. This type of vision is called mosaic vision. It is not especially sharp …
- CBSE 2026Set ANNUAL1 markMCQQ.The largest phylum of the Animal Kingdom is -(a) Chordata(b) Arthropoda(c) Annelida(d) Echinodermata
›Reveal solutionSolution
Arthropoda is the largest phylum of the Animal Kingdom, mainly because of the enormous diversity and number of insect species it contains.
Among the given options:
- Chordata includes animals with a notochord (fish to mammals) — a large but comparatively much smaller phylum.
- Arthropoda includes insects, crustaceans, arachnids and myriapods — jointed-legged animals with a chitinous exoskeleton.
- Annelida includes segmented worms like earthworm and leech.
- Echinodermata includes spiny-skinned marine animals like starfish and sea urchin. …
- CBSE 2025Set ANNUAL1 markMCQQ.Which creature can live for about a week without its head?(a) Frog(b) Earthworm(c) Pigeon(d) Cockroach
›Reveal solutionSolution
A cockroach can live for roughly a week without its head because it does not breathe through its head, and its nerve ganglia are distributed along its body rather than centralised solely in the head.
Unlike vertebrates, an insect such as a cockroach does not rely on its head for breathing — it takes in oxygen through small openings called spiracles located along the sides of its thorax and abdomen, connected to a network of tracheae that deliver oxygen directly to tissues, bypassing the need for lungs or a head-based respiratory centre. Its nervous system is also organised as a chain of ganglia (a 'ladder-like' nerve cord) running along the ventral side of the body, with each segment's ganglion able to control basic reflexes for that segment fairly independently of the brain.
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- CBSE 2025Set ANNUAL1 markMCQQ.Match the correct pair for Column 'A' term 'Arthropoda' from Column 'B'.(a) Sphagnum(b) Malpighian tubules(c) Trichoderma(d) Proboscis gland(e) Sequoia
›Reveal solutionSolution
Arthropoda matches with Malpighian tubules, their excretory organ.
Phylum Arthropoda is the largest animal phylum, characterised by a chitinous exoskeleton, jointed appendages, and an open (haemocoelic) circulatory system. Excretion in most terrestrial arthropods (like insects) occurs through thin, finger-like structures called Malpighian tubules that open into the gut and …
- CBSE 2023Set ANNUAL1 markMCQQ.To which phylum and class does Periplaneta belong?(a) Phylum-Annelida, Class-Reptilia(b) Phylum-Arthropoda, Class-Insecta(c) Phylum-Annelida, Class-Insecta(d) Phylum-Arthropoda, Class-Amphibia
›Reveal solutionSolution
Periplaneta (the cockroach) is classified under Phylum Arthropoda (jointed appendages, chitinous exoskeleton) and Class Insecta (three body regions, three pairs of legs, usually winged).
Periplaneta (the common cockroach) possesses a hard chitinous exoskeleton, a segmented body, and jointed appendages — the defining features of Phylum Arthropoda. Within this phylum, it belongs to Class Insecta, characterised by a body divisible into head, thorax and abd …
- CBSE 2022Set ANNUAL1 markMCQQ.Exoskeleton of which phylum consists of chitinous cuticle ?(a) Arthropoda(b) Annelida(c) Echinodermata(d) Porifera
›Reveal solutionSolution
Phylum Arthropoda is characterised by a hard, chitinous exoskeleton (cuticle) covering the body, which is periodically shed and replaced as the animal grows.
Arthropoda (from Greek 'arthron' = jointed, 'podos' = foot/leg) is the largest phylum in the animal kingdom, including insects, crustaceans, arachnids, and myriapods. A defining feature of this phylum is a tough, non-living external covering — the exoskeleton or cuticle — secreted by the underlying epidermis. This cuticle is composed mainly of chitin, a nitrogen-containing polysaccharide, often hardened further by proteins and, in crustaceans, by calcium salts. Because this exoskeleton is rigid and cannot grow with the animal, arthropods must periodically shed it and form a new, larger one in a process called ecdysis or moulting. By contrast, Annelida (segmented worms like earthworms) have a soft, moist cuticle without chitin and no jointed appendages; Echinodermata (starfish, sea urchins) have an interna …
- CBSE 2020Set ANNUAL1 markMCQQ.Mosaic vision is found in:(a) Cockroach(b) Bat(c) Fish(d) Human
›Reveal solutionSolution
Mosaic vision arises from compound eyes, a hallmark of arthropods like the cockroach.
A compound eye is made of numerous ommatidia (visual units), each of which captures a small part of the visual field. The brain assembles these many partial images into one composite 'mosaic' image, which is especially good at detecting motion.
- (a) Cockroach — has compound eyes → mosaic vision. Correct. …
- CBSE 2018Set ANNUAL1 markQ.Match the following. Column A item: 'Haemocoel'. Choose its correct match from Column B:(1) Casein(2) Water vascular system(3) Fixation of CO2(4) Bentham and Hooker(5) Cockroach
›Reveal solutionSolution
'Haemocoel' matches 'Cockroach' — arthropods like the cockroach have an open circulatory system in which blood fills a body cavity called the haemocoel.
In animals with a closed circulatory system (e.g., annelids, vertebrates), blood remains confined within blood vessels throughout the circuit. In contrast, arthropods such as the cockroach have an open circulatory system: blood (haemolymph) is pumped by a dorsal tubular heart into large, unenclosed body spaces called the haemocoel, where it directly bathes the internal organs and tissues before draining back toward the heart …
- CBSE 2017Set ANNUAL1 markQ.Name the excretory organ in Arthropodes.
›Reveal solutionSolution
Arthropods (e.g. cockroach, other insects) excrete nitrogenous waste through Malpighian tubules, thread-like structures that empty into the alimentary canal.
Malpighian tubules are numerous fine, blind-ending, thread-like tubules that arise at the junction of the midgut and hindgut and lie free in the body cavity, bathed in haemolymph.
- They absorb nitrogenous wastes (mainly uric acid) and other solutes directly from the surrounding haemolymph.
- The wastes are converted into and concentrated as semi-solid uric acid, which is passed into the hindgut and eliminated along with faecal matter through the anus. …
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