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.

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.

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.