Phylum Arthropoda


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Phylum Arthropoda: 

Phylum Arthropoda Dr. R. K Pillai, ‘Sneham’, Niranam North P.O., THIRUVALLA KERALA NEET-UG Presentation Diversity in Living World

General Characters: 

General Characters 1. Number of species 9,00,000. 2. ‘Arthropoda’ (Gr., arthros, jointed; podos, leg) the animals with jointed appendages. 3. Ernst von Siebold and H. Stannius (1845) established phylum ‘Arthropoda’. 4. The most successful group of animals.Their success due to unique jointed exoskeleton of cuticle. 5. Organ-system level of body organization. 6. Bilaterally symmetrical, triploblastic and metamerically segmented with tagmatization. 7. Segments not separated by septa as in annelids (only external segmentation). 8. Body divisible into 3 tagmata: head, thorax and abdomen. 9. Head and thorax fused in some forms to cephalothorax.

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10. Body cavity of a fluid filled haemocoel (sinuses or spaces in tissues). 11. Digestive system complete. 12. Mouthparts adapted for different modes of feeding. 13. Circulatory system open type. 14. Dorsal contractile heart, arteries and blood sinuses. 15. Respiration by: General body surface Gills Tracheae (air tubes) Booklungs 16. Excretory organs: Coxal, green (antennal) or maxillary glands Malpighian tubules 17. Major excretory product uric acid. 18. Nervous system with a dorsal nerve ring and a double ventral nerve cord. 19. Sense organs: Antennae Simple eyes Compound eyes Statocysts Chemoreceptors

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20. Sexes usually separate with paired reproductive organs and ducts. 21. Internal fertilization. 22. Majority are oviparous, 23. Scorpions ovoviviparous. 24. Development direct or indirect. 25. One to many larval stages, parthenogenesis in some. 26. For growth moulting or ecdysis.


Classification Phylum Arthropoda is divided into four subphyla:

Subphylum I ONYCHOPHORA (Gr., onyx, claw; pherein, to bear) : 

Subphylum I ONYCHOPHORA (Gr., onyx , claw; pherein , to bear) 1. The most primitive living arthropods. 2. Commonly called “velvet worms” or “walking worms”, about 70 species. 3. Body worm-like, claw bearing appendages (unjointed). e.g., Peripatus 4. Peripatus is a connecting link between arthropods and annelids.

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Subphylum II TRILOBITOMORPHA (Gr., tri, three; lobos, lobes; morphe, form): 

Subphylum II TRILOBITOMORPHA (Gr., tri , three; lobos , lobes; morphe , form) 1. The most primitive of all arthropods. 2. Fossil arthropods over 600 million years old. 3. Marine, abundant during the Cambrian and Ordovician period. 4. Name refers to the trilobed shape of the body.

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Subphylum III CHELICERATA (Gr., chele, claw; keras, horn; ata, group) : 

Subphylum III CHELICERATA (Gr., chele , claw; keras , horn; ata , group) 1. First pair chelicerae, second pair pedipalps. 2. Antennae absent, with six pairs of appendages. 3. Body divisible into: prosoma (cephalothorax) and opisthosoma (abdomen).

Class I Merostomata (Gr., meros, thigh; stoma, mouth) : 

Class I Merostomata (Gr., meros, thigh; stoma, mouth) 1. Aquatic, includes extinct giant aquatic Eurypterus (Cambrian to Permian) and horseshoe crabs. 2. Horseshoe crabs are known as “living fossils” they remain practically unchanged since Triassic period. 3. Only three genera (five species) survive today namely Limulus , Carcinoscorpius and Tachypleus .

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Class II Arachnida (Gr., arachne, spider) : 

Class II Arachnida (Gr., arachne , spider) 1. Terrestrial or aquatic, with six pairs of appendages. 2. Abdomen without appendages. 3. No wings, no antennae, many are predators. e.g. scorpions, spiders, mites and ticks. 4. Mites and ticks ectoparasites on other animals. 5. Most spiders spin a web to trap and capture prey. 6. The web made of silk produced by spinneret present in the posterior part of the abdomen. 7. Arachnida with four pairs of legs.

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Scorpion Spider

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Subphylum IV MANDIBULATA (L., mandibula, mandible; ata, group) Body divisible into head, thorax and abdomen, one or two pairs of antennae, a pair of jaws (mandibles), one or two pairs of maxillae.

Class I Crustacea (L., crusta, shell; acea, group) : 

Class I Crustacea (L., crusta, shell; acea, group) 1. Dominant arthropods of the sea. 2. With two pairs of antennae and biramous appendages. 3. Respiration by gills. 4. Respiratory pigment haemocyanin dissolved in plasma (metallic base copper). 5. Haemocyanin becomes light blue on oxygenation. 6. Stalked compound eyes. e.g. Prawns, lobsters and crabs

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cephalothorax Lobster

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Crab Squilla

Class II Myriapoda (Gr., myriad, ten thousand; podos, leg) : 

Class II Myriapoda (Gr., myriad, ten thousand; podos, leg) Includes millipedes and centipedes. Millipedes: Usually have 70- 100 pairs of legs. Two pairs of legs per segment (diplosegment). Herbivorous with no poison claws, simple eyes. harmless, coil into a tight spiral when disturbed.

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Centipedes: Usually have 10-30 pairs of legs. One pair of legs per segment. Carnivorous with a pair of poison claws. Simple eyes, capable of a painful, often poisonous bite. In centipede, the body is divided into head and trunk, thorax absent.

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Class III Insecta (L., insectus, cut into) : 

Class III Insecta (L., insectus , cut into) 1. Number of legs six, ‘Hexapoda’ (Gr., hexa , six; podos , leg) 2. With over 7,50,000 species grouped in 26 orders. 3. Insect form, the largest class of animals living on land and air. 4. One pair of antennae. 5. Body is divisible into three tagmata: head (6 segments) thorax (3 segments) abdomen (11 segments). 6. Respiration with tracheae. 7. Excretion by Malpighian tubules. 8. Excretory product is uric acid related with water conservation.

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Some Important Insects : 

Some Important Insects Lepisma (Silverfish) – A primitive wingless insect, without metamorphosis Grasshoppers and locusts – Phytophagous and gregarious Butterfly and moth – Complete metamorphosis Housefly and Mosquito – Two winged insects Fruitfly – Important in genetics Glowworm – Bioluminescent, sexual attraction Leaf insect – Famous for mimicry Ants, termites and – Colonial, social, honeybee polymorphic insects


Housefly Morphology 1. Musca domestica is the most common housefly in Europe and America. 2. The commonest Indian species Musca nebula. 3. Housefly, a diurnal insect (active during day time). 4. Body divided into head, thorax and abdomen. 5. Head is large with a pair of compound eyes (4000 ommatidia), three ocelli and two antennae. 6. Antenna, three-segmented structure with basal scape, middle pedicel and terminal flagellum. 7. The flagellum bears a brush-like process called arista. 8. Thorax is three-segmented with: three pairs of legs one pair of wings (mesothoracic) a pair of halteres

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Life History of Housefly

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9. Halteres are present on metathorax and are balancing organs during flight. 10. Housefly while sitting, all the three pairs of legs rest on the surface (in mosquito, metathoracic legs do not touch the ground. Mouthparts 1. Sponging type, adapted for sucking liquid or semiliquid. 2. Labium , the most developed component of mouthparts forming the proboscis. 3. Proboscis with three regions : Rostrum (Basiproboscis) Haustellum (Mediproboscis) Labellum (Distiproboscis) 4. Oral groove on haustellum with blade-like hypopharynx (with salivary duct) and flattened labrum plus epipharynx. 5. Food channel formed by labrum plus epipharynx and hypopharynx.

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6. Pseudotracheae (very fine longitudinal slits) found in labellum. 7. All pseudotracheae converge and lead into a preoral aperture. 8. Preoral aperture is surrounded by minute hair-like prestomial teeth. 9. In the mouthparts of housefly, mandibles are totally absent. 10. Maxillae are represented by a pair of small unjointed palps. 11. Houseflies are saprophagous, feed upon all sorts of dead organic matter. Housefly feeds only when food is in liquid state. Lifehistory 1. Breeding occurs in summer and rainy season (March to October). 2. Lays eggs on decaying organic matter such as cow dung, horse manure, human faeces, etc.

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3. Number of eggs laid is about 500-600 during lifespan in a month. 4. Eggs, shiny white, slightly curved and elliptical in shape, hatch in 12 to 24 hours. 5. A larval stage occurs called maggot. 6. Maggot moults twice, thus housefly has three larval instars. 7. First instar larva is 2 mm in length consisting of 13 segments. 8. The first segment is pseudocephalon with a pair of oral lobes, mouth guarded by a pair of mandibular sclerites (hooks), optic tubercles. 9. 6th to last body segments (2 to 9th abdominal segments) bear spiniferous pads locomotory in function. 10. Last (13th) segment bears a pair of posterior spiracles, anus and two anal lobes. 11. First instar larva has only one pair of posterior abdominal spiracles so it is metapneustic. 12. Second instar larva of housefly has one pair of abdominal and one pair of prothoracic spiracles, amphipneustic.

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13. Third instar larva becomes about 6-12 mm in length. 14. Larva of housefly respires by means of tracheae . 15. The third instar maggot is transformed into pupa. 16. Total larval period in housefly is normally 6-8 days. 17. Pupa is covered by pupal case or puparium. Within pupa histolysis and histogenesis takes place. 18. An imago (young one of housefly) will come out after 4- 5 days. 19. Hatching of maggot from the egg of a housefly is a good example of metamorphosis. 20. Housefly shows a complete metamorphosis (holometabolous type). 21. Different stages in the life history of housefly are: Egg–Larva (maggot)–Pupa–Imago (adult). 22. Housefly is a curse to mankind, some dangerous diseases are spread by housefly. 23. Myiasis is a disease caused by maggots.

Diseases Spread by Housefly: 

Diseases Spread by Housefly Anthrax Trachoma Diarrhoea Tuberculosis Leprosy Gangrene Plague Gonorrhoea Typhoid Cholera Dysentery


Mosquito Morphology 1. Mosquito is a two-winged insect (also housefly and fruitfly). 2. The common genera of mosquito are: Culex (body held parallel to surface while sitting) Aedes (= Stegomyia ) (body held parallel to surface while sitting, with black and white striped body) Anopheles (Body held at an angle to the surface, dark spotted wing) 3. Female mosquitoes are blood suckers of vertebrates while the male sucks the plant juice. 4. Female mosquito is an ectoparasite (sanguivorous) and it is also an intermediate host for the pathogens like Plasmodium and Filaria .

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Culex Eurypterus Anopheles

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5. Plasmodium can be called as a hyperparasite, because its host mosquito is a parasite. 6. Like other insects, the body of mosquito is divisible into head, thorax and abdomen. 7. Head bears a pair of antennae, compound eyes and mouth- parts. 8. In adult mosquito, ocelli (simple eyes) are totally absent (in cockroach and housefly, ocelli are present). 9. Thorax is three-segmented with only one pair of wings (mesothoracic). Metathoracic wings are modified into halteres which are balancing and sound producing structures. 10. Mosquito shows sexual dimorphism. Sex differentiation can be done on the basis of antennae and maxillary palps. 11. Antenna of a male mosquito is plumose (more hairy or brushy)and female is pilose (with few short hairs). 12. Maxillary palp is as long as proboscis in both sexes but club-shaped in male Anopheles . 13. Maxillary palp is three-jointed, smaller than proboscis and clubbate in female Culex .

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Mouthparts 1. Female mosquitoes are blood suckers, have piercing and sucking mouthparts. 2. Mouthparts found in both sexes are: Labrum plus epipharynx forming upper lip and labium and its two labellae form proboscis. 3. Mouthparts of female: (i) Hypopharynx (1) injection needle-like with central salivary duct running through it. Saliva contains anti- coagulant. (ii) Mandibles (2) needle-like with serrated broad saw- shaped. (iii) Maxillae (2) needle-like with sharp blades at tip. The puncturing elements in the mouthparts of female mosquito are maxillae and mandibles. 4. Mouthparts of male: (i) Hypopharynx– less developed, fused with labium. (ii) Mandibles are totally absent. (iii) Maxillae are reduced. 5. Food channel is formed by labrum plus epipharynx and hypopharynx.

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Life Cycle 1. Male and female mosquito copulate while in flight (as in honeybee). 2. Fertilized eggs are laid on stagnant water surface. 3. Mosquito undergoes a complete metamorphosis. 4. The larva of mosquito is also known as ‘wriggler’. 5. Wriggler is a free swimming; active and aquatic larva performing wriggling movements. 6. The body has head, thorax (without legs) and abdomen (9-segmented). 7. Head bears a pair of compound eyes, a pair of simple eyes (absent in adult mosquito), a pair of small antennae. 8. Wriggler has a lifespan of 3-4 days. 9. During this period, it undergoes four moults to give rise to five instar larva. 10. If all water reservoirs (ponds etc.) get dry, chances of dissemination of malarial parasites are minimized as the larval stages of mosquito will die causing no survival of mosquitoes.

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11. Spraying of oil on stagnant water controls malaria because mosquito larvae cannot breathe and die. 12. Fish which can be used in biological control of mosquitoes is Gambusia . 13. The pupa of mosquito is known as tumbler. 14. 5th instar larva changes into a pupa (nonfeeding), it is comma-shaped. 15. Pupa has cephalothorax and abdomen (9-segmented, ventrally flexed). 16. It has a pair of respiratory trumpets. 17. Tumbler has a life span of 2-7 days (in Musca 4-5 days). 18. After completion of metamorphosis, it will transform into an adult called ‘Imago’. 19. Female mosquito lives for a month or more and the male is about a week. 20. Johnston’s organ lies in the second segment of antennae. In male mosquito, it helps to locate females by flight tone.

Mosquito Born Diseases : 

Mosquito Born Diseases Disease Pathogen Mosquito Malaria Plasmodium Anopheles female Filariasis Wuchereria Culex female Encephalitis Virus Culex and Aedes female Dengue fever Virus Aedes female Yellow fever Virus Aedes female

Economic Importace of Insects: 

Economic Importace of Insects 1. The injurious and beneficial insects are of great economic importance and their study is known as ‘Economic Entomology’. 2. Injurious insects or harmful insects are: Pests of agriculture Pests of store-grains Household pests Pests of domestic animals Disease carriers Poisonous insects

Store-grain pests: 

Store-grain pests Rice weevil Sitophilus oryzae Wheat weevil Trogoderma granarium Red flour beetle Tribolium confusum Pulse beetle Callosobruchus chinensis

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Rice weevil Red flour beetle Wheat weevil Pulse weevil

Household Pests: 

Household Pests Cockroaches Periplaneta Houseflies Musca Mosquitoes Anopheles, Culex & Aedes Bedbugs Cimex Termites Odontotermes


Termite 1. Termite is an injurious colonial social, polymorphic insect, with division of labour. 2. The home of termite is termitarium. 3. Termites shows caste system, the main castes are : kings, queens, workers and soldiers. 4. Queen has a prominent and extended abdomen, it is an ‘egg laying machine’. 5. Trichonympha, a flagellate protozoan is found in the gut of termite; it digests cellulose (symbiosis).

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Insect Disease Carriers: 

Insect Disease Carriers Insect Diseases 1. Housefly Anthrax, Trachoma, Diarrhoea, Tuberculosis, Leprosy. Gangrene, Plague, Gonorrhoea,Typhoid, Cholera, Dysentery, etc. 2. Mosquitoes Malaria, Filariasis, Encephalitis, Dengue fever, Yellow fever, etc. 3. Kissing bug Chagas’ disease 4. Rat flea Bubonic plague 5. Deerfly Tularemia 6. Sandfly Kala-azar (Visceral leishmaniasis) 7. Tsetse fly African sleeping sickness 8. Bedbug Typhus fever 9. Head louse Trench fever 10. Body louse Relapsing fever

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Kissing bug Rat flea Deerfly Sandfly

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Tsetsefly Bedbug Head louse Body louse

Beneficial Insects: 

Beneficial Insects Scavengers 1. Scavenger insects which feed on the waste materials such as dead bodies and debris of plants and animals. e.g., Silverfishes, termites, houseflies, dung beetles, ants, cockroaches, etc. Pollinators of Flowers 2. These insects help in the pollination of flowers. e.g., Bees, wasps, butterflies. 3. Productive Insects: Honeybees, silkmoths and lac insects are important, Productive insects Commercial products of these insects are: Honeybee – Honey and wax Silkmoth – Silk Lac insect – Lac


Honeybee 1. Honeybees are colonial, social, polymorphic insects with a division of labour. 2. A colony of honeybee consists of three castes, viz., queen, drone and worker. 3. Different species of honeybee are: Apis mellifera – European bee Apis dorsata – Rockbee – largest Apis indica – Indian bee Apis florea – Little bee – smallest 4. Honeybees are domesticated insects, feed on nectar and pollen. 5. Bee rearing or bee keeping is called ‘apiculture’. 6. Mouthparts of honeybee are ‘chewing and lapping type’.

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Honey Bee

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7. Honeybee shows both sexual and asexual (parthenogenetic) reproduction . 8. Diploid (2n = 32) fertilized eggs give rise to queen and workers and unfertilized haploid (n = 16) produce males or drones 9. Natural parthenogenesis occurs in honeybee . 10. Haploid parthenogenesis in honeybee is called as arrhenotoky . 11. Queen bee is a fertilized female developed from the larva hatched from fertilized egg which is fed on ‘royal jelly’. 12. ‘Royal jelly’ is secreted by worker; it is digested honey, pollen and secretion of maxillary gland. 13. All larvae receive it for two days and queen receives it throughout life. 14. Bee wax is a secretory product of hypodermal glands of the abdomen of worker bee. 15. Queen bee is a specialized organism for egg-laying. 16. Honey is a product of regurgitation of nectar from crop; sucrose is hydrolysed into monosaccharides like glucose, levulose and fructose. 17. The sting of honeybee worker is a modified ovipositor.

Bee dance: 

Bee dance 1. Highest development of communication is found in honeybee. 2. Honeybees communicate to other members of the colony by dance and sound. 3. Karl von Frisch (1946-69) decoded the language of dance by bees. 4. Karl von Frisch (the zoologist from Austria) got Nobel Prize in 1973 on the work of bee dance. 5. According to Wenner (1964) in addition to dance, honeybee communicates by sound. 6. By sound, richness of food source will be made known. 7. Bee messages include: 1. Source of food supply 2. Food source direction in relation to sun and distance from the colony 3. Richness of source. 8. The messages were carried by dance and sound vibrations of scout bee.

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Bee Dance

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Round Dance 1. The source of food is near the hive (less than 75 meter), no indication of direction of source. Tail Wagging Dance 2. Long distance source, convey distance of new source and also its direction in relation to position of sun. 3. Tail wagging straight run directed vertically upwards, the food is located straight towards the sun. 4. Tail wagging run directed vertically downwards, the food source is located straight in opposite to sun. 5. Tail wagging run at an angle, the source is at angle with reference to sun. 6. Foraging bee gets communication from scout bee by contact, visual and sound. 7. Smell of the flowers and earlier bee guides the subsequent bee to visit the same food source. 8. Honeybee is one of the most important pollinator in agriculture.

Silk Moth: 

Silk Moth 1. Silk is produced by an insect called silk moth. 2. Rearing of silkworm for commercial production of silk is called ‘sericulture’. 3. Bombyx mori is the mulberry silkworm. 4. Caterpillar feeds on mulberry leaves , its salivary gland secretes liquid silk. 5. The salivary gland (= labial gland) is modified forming silk gland of the larva. 6. Silk is obtained from cocoon (pupa, chrysalis). 7. Ripe cocoons are treated with boiling water to kill the moth before hatching . 8. Silk thread is formed of two proteins namely fibroin and sericin. 9. Natural silk contains nitrogen. 10. Mysore is the biggest centre for the production of raw silk in India. 11. Central Sericulture Institute is situated in Berhampore.

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Silk Moth (Adult)

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Life History of Silk Moth

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LAC INSECT 1. Lac is produced commercially by an insect Tachardia lacca ( Laccifer lacca ). 2. Lac is actually secreted for its protection and not for the food of the insect. 3. Male insects are winged and structurally complete, but females are degenerated. 4. Lac or shellac is an exuviate (secretion) of mainly female. 5. Lac is a resinous substance. COCHINEAL BUG Dactylopis coccus lives upon cactus; dead and dried bodies are used for making a dye called cochineal. BLISTER BEETLE 1. Lytta is a genus of blister beetle; the drug cantheridine is prepared from its blood. 2. Cantheridine is widely used for healthy growth of hair. RED ANTS Red ants are used for the production of formic acid.

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Lac Insect

Important Larvae: 

Important Larvae 1. Nauplius – Crustacea 2. Zoaea larva – Crustacea 3. Mysis larva – Crustacea 4. Megalopa larva – Crustacea 5. Phyllosoma larva – Crustacea 6. Alima larva – Crustacea 7. Caterpillar – Butterfly 8. Maggot – Housefly 9. Wriggler – Mosquito 10. Grub – Beetle

Mouthparts in Insects: 

Mouthparts in Insects 1. Biting and chewing – Cockroach and grasshopper 2. Chewing and lapping – Honeybee 3. Piercing and sucking – Mosquito and bug 4. Sponging – Housefly 5. Siphoning – Butterfly

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Mouthparts of Insects

Taxonomic Summary: 

Taxonomic Summary Phylum Arthropoda Subphylum ONYCHOPHORA Peripatus — Velvet worm / Walking worm Subphylum TRILOBITOMORPHA Subphylum CHELICERATA Class Merostomata Eurypterus — Giant water scorpion (extinct) Limulus — Horseshoe crab/ Kingcrab (Living fossil) Class Pycnogonida Nymphon — Sea spider Class Arachnida Palamnaeus — Scorpion Lycosa — Spider Ixodes — Sheeptick Sarcoptes — Itch mite

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Eurypterus fossil

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Subphylum MANDIBULATA Class Crustacea Astacus — Crayfish Argulus — Carp lice Daphnia — Waterflea Palaemon — Freshwater prawn Penaeus — Marine prawn Panulirus — Lobster Squilla — Mantis shrimp Lucifer — Shrimp Oniscus — Wood lice Carcinus — Crab Hippa — Mole crab Eupagurus — Hermit crab Balanus — Rock barnacle (Acorn shell) Lepas — Goose barnacle Class Myriapoda Julus — Millipede Scolopendra — Centipede

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Crayfish Waterflea Prawn Shrimp

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Class Insecta Lepisma — Silverfish Carausius — Stick insect Phyllium — Leaf insect Pediculus — Louse Cimex — Bedbug Xenopsylla — Ratflea Drosophila — Fruitfly Musca — Housefly Phlebotomus — Sandfly Glossina — Tsetsefly Bombyx — Silkmoth Apis — Honeybee

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Silverfish Stick insect Leaf insect Fruit fly

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A true Objective Hand Book “A conscientious teacher of Zoology who has been guiding students for various competitions for last 30 years has put his best in this book” 11 th Edition

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End Thanks