The document discusses the phylum Arthropoda, which includes insects, arachnids, crustaceans, and others. It describes their key characteristics, including a jointed exoskeleton, bilateral symmetry, and bodies divided into segments. Arthropods live in many habitats and have adaptations for respiration, circulation, reproduction, and other functions. The largest class is Insecta, including over 750,000 species, while other classes include crustaceans, centipedes, millipedes, and arachnids. Common examples of arthropods from each class are also provided.

1. ARTHROPODA: HOW TO EXPLAIN
THE LARGEST PHYLUM
Phylum arthropoda consists of the animals with jointed legs. In animal kingdom it represents
maximum number of species. It includes crabs, prawns, insects, spiders, scorpions, ticks,
mites, centipeds, millipeds.
GENERAL CHARACTERS OF ARTHROPODA
 HABITAT : They are found in all types of habitat like aquatic or terrestrial, sometime
aerisal also.
 SYMMETRY : They are bilaterally symmetrical.
 GERM LAYERS : Triploblastic with organ system level of organisation.
 BODY REGION : It is divided into three regions like head, thorax, abdomen.
 APPENDAGES : Paired jointed appendages or feet are present which are modified for
feeding, walking, swimming etc. Cilia is absent in this phylum.
 EXOSKELETON: The body is covered with a thick, tough and non-living chitinous cuticle,
which form the exoskeleton. It is made up of protein and a special type of nitrogenous
polysaccharide named chitin.
 BODY CAVITY : The coelome is greatly reduced and filled with blood and we term them
as haemocoel.
 DIGESTIVE TRACT : Complete alimentary canal comprises three regions
like stamodeum (foregut), mesenteron (midgut), protodeum(hindgut). Mouth contains
movable parts called pincers or chelicerae. These do chewing, sucking, piercing,
sponging etc.
 RESPIRATION : In aquatic form the organ is gills and in terrestrial form the organs are
book-lung or trachea.
 CIRCULATORY SYSTEM : Blood flows in the haemocoel instead of blood vessel . So we
term it as open circulatory system. Blood is colorless and contains white corpuscles so
we named it haemolymph.
 EXCRETORY SYSTEM : Green glands or malpighian tubules are the excretory organs.
 NERVOUS SYSTEM : It consists of a nerve ring and double ganglionated ventral nerve
cord.
 SENSE ORGANS : Arthropoda contains compound eye which contains many similar
units called ommatidia. One or two pairs of antenae are present as feelers in many
forms. Aquatic form may have statocyst for balancing.
 ENDOCRINE SYSTEM : Arthropoda are first animal having endocrine system. Some
animals release pheromone used for sex attraction.
 REPRODUCTION : It may be outside of the body (external) or inside of the body
(internal). They may be oviparous or viviparous. Some arthropoda develops new
offspring without fertilization called parthenogenesis.
CLASSIFICATION OF ARTHROPODA
This phylum is divided into six classes: Onychphora, Crustacea, Chilopoda, Diplopoda,
Insecta, Arachnida.
CLASS : Onychophora: They occur in moist habitat and have worm like segmented body .
body bears unjointed legs with claws. Example : Peripetus( connecting link between
annelida and arthropoda) it is also known as walking worm. It is a terrestrial segmented
worm like arthropoda. They show characters of annelida like jointed, parapodia like legs,
nephridia for excretion and simple gut.

2. CLASS : Crustacea : They are aquatic arthropods with body divisible into cephalothorax
(head + thorax + abdomen) . Excretion takes place through green glands. Example
: Daphnia or water flea, Prawn, Crab.
CLASS : Chilopoda: Flattened body with two region head and trunk. Excretion occurs by
malpighian tubules. Example Centipeda.
CLASS : Diplopoda: Body is long cylindrical and divisible into three regions head, thorax and
abdomen. Each thoracic segment except the first bears a pair of legs while each abdomen
segment has two pairs of legs. Example Milliped.
CLASS : Insecta : It is the largest class of animals including more than 7,50, 000 species.
They live on land and in air. Many have become secondarily aquatic. Insects are the most
successful land invertebrate and the only competitors with humans for dominance.
The insect body is divisible into three regions : head, thorax, abdomen. Head bears a pair of
antenae, a pair of compound eyes and mouth parts adapted for various modes of feeding.
Thorax consists of three segments each with a pair of legs (six legged), the second and third
segments may have wings. Abdomen consists of 11 segments. Respiration occurs through
tracheae. Excretory organs are the malpighian tuules, which opens into digestive tract. Sexes
are separate. They are oviparous that means oviparous. Development often include a larval
stage and metamorphosis. Example silver fish, cockroach, termite, honey bee, head lice,
rat flea, silk moth, house fly, mosquito, wasp, aphides, beetles, butter fly, locust.
SIMPLE QUESTIONS ON ARTHROPODA
Qs1: State the difference between centipedes and millipede in body structure , antenae,
nutrition and stink gland.
Ans2:
TOPIC CENTIPEDES MILLIPEDES
Body structure Dorsiventrally flattened Cylindrical
Antenae Long and tapering Short and club shaped
Nutrition Carnivorous Herbivorous
Stink gland Absent Emits a foul smelling
Qs2:Name one wingless primitive insect form.
Ans2: Silver fish.
Qs3: Name the insect whose wings are not folded.
Ans3: Dragon fly and Dasmel fly.
Qs4: Name the winged insect that can fold their wings over their backs and exhibit incomplete
metamorphosis.
Ans4: Grasshoppers, Locusts, Cockroach, Termites.
Qs5: Name the winged insect which fold their wings and exhibit complete metamorphosis.

3. Ans5: Honey bees, Butterfly, Moths, Flies, Mosquito.
Qs6: Name the mouth parts of insect.
Ans6: One labrum, One labium, one hypopharynx, Two mandibles, Two maxillae,
Qs7: Mention three habits of Periplaneta americana.
Ans7: Periplaneta americana or cockroach is nocturnal, omnivorous, cannibalism.
Qs8: What is the special life span for male and female Bombyx mori.
Ans8: Bombyx mori or silk moth has special type of life span. Male silk moth dies soon
after copulation. Female silk moth die after laying eggs.
Qs9: What do you know about drone and worker?
Ans9: Male bee is drone who can fertilize queen female bee. Workers are sterile female
having sting at the posterior end of the body.
Qs10: Why is Peripatus known as connecting link?
Ans10: Peripatus or walking worm is a terrestrial segmented worm like arthropod,
found in the crevices of rocks and under the stones. This worm has jointed parapodia
like legs, nephridia for excretion like annelida.
Qs11: Justify the statement arthropoda has advancement over annelida.
Ans11: The arthropoda shows advancement over annelida, as they have distinct head,
jointed apendages modified for various functions, jointed exoskeleton, special
respiratory organs, well developed sense organs and secretion of pheromones for
communication.
Qs12: State the characteristics of Scolopendra.
Ans12: Scolopendra or centipede is found in humid places, under stones, decaying
wood, bark. It is nocturnal, carnivorous and swift swimmer. It kills its prey with poison
claws and also gives a poisonous bite to its enemies.