In this article we will discuss about Arthropoda:- 1. General Characters of Arthropoda 2. Classification of Arthropoda.
General Characters of Arthropoda:
1. Arthropods are triploblastic, bilaterally symmetrical, metamerically segmented animals.
2. Body of Arthropoda is covered with a thick chitinous cuticle forming an exoskeleton.
3. Body segments usually bear paired lateral and jointed appendages.
4. Musculature is not continuous but comprises separate striped muscles.
5. Body cavity is haemocoel. The true coelom is reduced to the spaces of the genital and excretory organs.
6. Digestive tract is complete, mouth and anus lie at opposite ends of the body.
7. Circulatory system is open with dorsal heart and arteries but without capillaries.
8. Respiration through general body surface, by gills in aquatic forms, tracheae or book lungs in terrestrial forms.
9. True nephridia are absent; excretion by coelomoducts or Malpighian tubules or green or coxal glands.
10. Cilia are entirely absent from all parts of the body.
11. Sexes are generally separate and sexual dimorphism is often exhibited by several forms.
12. Fertilisation is internal. Development is usually indirect through larval stages.
13. Parental care is also often well marked in many arthropods.
14. Most diversified group inhabiting the land, water and air.
Classification of Arthropoda:
Phylum Arthropoda and its various groups have been classified differently by different workers. But the classification of Arthropoda followed in the present text is generally based on Vandel (1949), Snodgrass (1960) and Storer (1979).
Onychophora, however, was considered to be arthropod for a long time but the modern trend is to consider it as an independent group of segmented animals.
Subphylum I. Trilobitomorpha:
(Gr., tria = three + lobos = lobe + morphe – form):
1. Represented by fossil trilobites only.
2. Body separated by two longitudinal furrows into three lobes.
3. Except the last segment all segments bear biramous appendages.
4. All were marine forms.
5. All were bottom dwellers, i.e., benthozoic and existed from Cambrian to Permian.
Examples:
Triarthrus, Dalmanites.
Subphylum II. Chelicerata:
(Gr., chele = claw + keros = horn + ata = group):
1. Body divisible into cephalothorax or prosoma and abdomen or opisthosoma.
2. First pair of appendages are chelicerae which are preoral and feeding in function.
3. Second pair of appendages are pedipalpi which are postoral.
4. Antennae and true jaws not found.
5. Mostly terrestrial and predaceous.
Class 1. Merostomata:
1. Exclusively aquatic, all marine.
2. Prosoma bears compound eyes placed laterally; it is broadly jointed to abdomen.
3. Five or six pairs of appendages in abdomen modified as gills or branchiae for respiration.
4. Abdomen ends in a spike-like long telson.
Subclass I. Xiphosura:
1. Prosoma is convex covered by a broad horse-shoe-shaped carapace.
2. Prosoma bears six pairs of appendages.
3. Opisthosoma hexagonal consisting of six mesosomatic segments and a vestigial un-segmented metasoma with a long narrow telson.
4. Genital openings paired covered by genital operculum.
5. Respiration by lamelliform gills or book- gills attached to the abdominal appendages.
Example:
Limulus (King crab).
Subclass II. Eurypterida:
1. Extinct (Palaeozoic) forms.
2. Large sized arthropods.
3. Cephalothorax small covered by dorsal carapace.
4. Cephalothorax followed by 12 free segments and a terminal elongated narrow telson.
5. Cephalothorax with six pairs of appendages.
Examples:
Eurypterus, Pterygotus.
Class 2. Arachnida (Gr., arachne = spider + oid = like):
1. Mostly terrestrial, few aquatic.
2. Prosoma bears six pairs of appendages; one pair chelicerae one pair pedipalpi and four pairs of walking legs.
3. Abdomen usually without appendages.
4. Respiratory organs either tracheae, book- lungs or book-gills.
5. Excretory organs are Malpighian tubules or coxal glands or both.
6. Sexes are separate, sexual dimorphism not conspicuous and development mostly direct.
Order 1. Scorpionida:
1. Terrestrial forms found under stones in tropical and subtropical regions; true scorpions.
2. Prosoma covered dorsally by carapace and bears a pair of chelicerae, a pair of pedipalpi and four pairs of walking legs.
3. Opisthosoma divisible into mesosoma and metasoma; mesosoma is broad consisting of seven segments and metasoma is narrow consisting of five segments with a poison- sting.
4. A pair of comb-like pectines occur ventrally on the second segment of mesosoma.
5. Respiration by four pairs of book-lungs.
Examples:
Buthus, Palamnaeus.
Order 2. Pseudoscorpionida:
1. Minute false scorpions found under the bark of trees.
2. Prosoma formed of six fused segments covered dorsally by carapace.
3. Opisthosoma often to twelve segments.
4. Sting and telson not found.
5. A pair of spinning glands present.
6. Respiration by tracheae.
Example:
Chelifer.
Order 3. Palpigradi:
1. Small arachnids.
2. Opisthosoma often segments and is jointed to the prosoma by a pedicle.
3. Telson with a long jointed flagellum.
4. Chelicerae are chelate and pedipalpi leg like.
5. Respiration by three pairs of book-lungs.
Example:
Koenenia.
Order 4. Solifugae:
1. Body consists of prosoma and opisthosoma.
2. Prosoma consists of three fused and last three segments.
3. Opisthosoma composed of ten segments and is not marked off from prosoma.
4. Chelicerae are large and chelate, pedipalpi are elongated and leg-like.
5. Poison glands absent.
6. Respiration by tracheae.
7. Commonly referred to as sun spiders or wind spiders.
Example:
Galeodes.
Order 5. Amblypygi:
1. Somewhat flattened body.
2. Carapace covering the prosoma undivided.
3. Pedipalpi large and heavy, chelicerae of moderate size.
4. First pair walking legs sensory in nature.
5. Opisthosoma bears twelve segments, flagellum absent.
Example:
Charinus.
Order 6. Uropygi:
1. Commonly referred to as whip scorpions.
2. Chelicerae two-jointed and moderate in size.
3. Pedipalpi large, heavy and usually with pincers.
4. Opisthosoma bears twelve segmentsa long flagellum present in the last segment.
5. Eyes one pair.
Examples:
Thelyphonus, Mastigoproctus.
Order 7. Araneae:
1. Body consists of prosoma and opisthosoma.
2. Prosoma is unsegmented covered by carapace and bears six pairs of appendages.
3. Opisthosoma is usually unsegmented attached to prosoma by a narrow pedicle.
4. Chelicerae are subchelate with poison glands.
5. Pedipalps simple and six jointed.
6. Eight eyes are arranged dorsally in two rows on the carapace of prosoma.
7. Respiration either by book-lungs or book- lungs and tracheae both.
8. True spiders.
Examples:
Argiope (Writing spider), Aranea (House spider) Lycosa (Wolf spider), Agelena (Funnel-web spider).
Order 8. Ricinulei:
1. Body consists of prosoma and opisthosoma.
2. Prosoma with movable anterior cucullus.
3. Opisthosoma composed of nine segments and connected to prosoma by a pedicle.
4. Chelicerae and pedipalpi are chelate.
5. Respiration by tracheae.
Examples:
Cryptocellus, Ricinoides.
Order 9. Phalangida or Opiliones:
1. Spider-like in appearance.
2. Prosoma unsegmented, opisthosoma bears ten segments.
3. Pedicel absent between prosoma and opisthosoma.
4. Chelicerae chelate; pedipalpi leg-like.
5. Spinning glands not found.
6. Respiration by tracheae.
Examples:
Phalangium, Leiobunum.
Order 10. Acarina:
1. Body unsegmented in which prosoma is fused with opisthosoma.
2. Chelicerae and pedipalpi are small and associated with the mouth-parts which are adapted for biting, piercing and sucking.
3. Respiration by tracheae or by skin.
4. Free living and parasitic forms.
5. Commonly referred to as ticks and mites.
Examples:
Chorioptes (Mite), Sarcoptes (Itch-mite), Idodex (Tick).
Class 3. Pycnogonida:
1. Commonly referred to as sea spiders.
2. Very small in size.
3. Body mainly consists of cephalothorax, abdomen reduced.
4. Pedipalpi short segmented and chelicerae very small.
5. Usually eight pairs of long walking legs.
6. Mouth placed on a long proboscis.
7. Eyes simple and 4 in number.
8. Respiratory and excretory organs wanting.
9. Sexes separate (dioecious); females with a pair of ovigers for carrying eggs.
Examples:
Pycnogonum, Nymphon.
Subphylum III. Mandibulata:
(L., mandibula = mandible + at a = group):
1. Terrestrial and aquatic both freshwater and marine.
2. Body divisible into either cephalothhorax and abdomen or head, thorax and abdomen.
3. Appendages of head consist of one or two pairs of antennae, one pair of mandibles and one or two pairs of maxillae.
4. Eyes usually compound.
5. Respiration either by gills or tracheae.
6. Excretion by Malpighian tubules or green glands.
7. Sexes usually separate with sexual dimorphism.
8. Development usually involves larval stages.
Class 1. Crustacea (L., crusta = a hard shell):
1. Mainly aquatic, generally marine but few freshwater and few live in moist places.
2. Generally free living but few are parasitic forms.
3. Head often fused with thorax to form cephalothorax covered dorsally by carapace.
4. Head bears a pair of compound eyes and five pairs of appendages.
5. Thorax and abdomen often with a pair of biramous appendages in each segment; appendages modified for various purpose.
6. Respiration either by gills or general body surface.
7. Coelom greatly reduced, it is in the form of haemocoel.
8. Blood vascular system comprises a dorsal contractile heart communicating by valvular ostia with an enclosing pericardial sinus.
9. Excretory organs are modified coelomoducts which may be either maxillary glands or antennary (green) glands.
10. Sexes usually separate; sexual dimorphism is common.
11. Development includes metamorphosis with free larval stages.
Subclass I. Cephalocarida:
1. Body divisible into a horse-shoe-shaped head and trunk; trunk bears 19 segments.
2. Eyes and carpace not found.
3. Head bears 2 pairs of antennae, a pair of jaws and 2 pairs of maxillae.
4. Anterior nine trunk segments bear appendages which appear triramous.
5. Monoecious forms, genital opening on the 19th segment.
6. Marine and bottom dweller forms.
Example:
Hutchinsoniella.
Subclass II. Branchiopoda:
1. Freshwater, free-living, small-sized forms.
2. Carapace either shield-like or bivalved shell-like or even absent.
3. Thoracic appendages flattened, lobed and leaf-like provided with bristles.
4. Appendages are usually for locomotion and filter feeding; they also serve as gills.
5. Abdomen devoid of appendages but bears a pair of caudal stylets.
6. Antennules and maxillae reduced or absent.
7. Parthenogenesis is very common.
8. Larva is nauplius.
Order 1. Anostraca:
1. Body elongated, carapace not developed.
2. Eyes stalked.
3. Antennae uniramous.
4. Caudal stylets unjointed.
5. Commonly called fairy shrimps.
Examples:
Branchipus, Eubranchipus.
Order 2. Notostraca:
1. Body elongated, carapace broad shield- shaped.
2. Eyes without stalk (sessile).
3. Antennae reduced, anterior half of trunk bears 35-70 pairs of appendages.
4. Caudal stylets many-jointed.
5. Commonly called tadpole shrimps.
Examples:
Apus, Lepidurus.
Order 3. Diplostraca:
1. Body laterally compressed.
2. Carapace usually transparent bivalved shell covering the body but not the head.
3. Eyes sessile and usually united together.
4. Antennae biramous, large and used for swimming.
5. Caudal stylets unjointed, curved, claw-like.
6. Commonly called clam-shrimps or water- fleas.
Examples:
Daphnia, Limentis.
Subclass III. Ostracoda:
1. Small crustaceans found both in freshwater and sea.
2. Body laterally compressed not distinctly segmented.
3. Body enclosed in bivalved shell.
4. Two pairs of stout and cylindrical thoracic appendages.
5. Antennules and antennae used in swimming.
6. Mandibles are provided with palps.
7. Parthenogenesis is of common occurrence.
8. Commonly called seed-shrimps.
Order 1. Myodocopa:
1. Found in sea water.
2. Carapace notched with apertures for antennae.
3. Second antennae biramous with a large basal segment.
4. Second antennae used in swimming.
Examples:
Cypridina, Phylomedes.
Order 2. Platycopa:
1. Found in sea water.
2. Carapace not notched without apertures for antennae.
3. Second antennae uniramous.
4. Trunk appendages one pair.
5. Antennae not used in swimming.
Example:
Cytherella.
Order 3. Podocopa:
1. Both marine and freshwater forms.
2. Carapace unnotched without apertures for antennae.
3. Second antennae uniramous, leg-like with claws at the tips
Examples:
Cypris, Darwinula.
Order 4. Cladocopa:
1. Found in sea water.
2. Carapace unnotched without apertures for antennae.
3. Second antennae biramous.
4. Both pairs of antennae used in swimming.
Example:
Polycope.
Subclass IV. Mystacocarida:
1. Small-sized crustaceans with elongated body divisible into head, five-segmented thorax and six-segmented abdomen.
2. Head appendages well developed as also is the first thoracic pair (maxillipedes).
3. Abdominal appendages wanting except a pair of caudal stylets in the last segment.
4. Sexes separate.
5. Metanauplius is the earliest known larval stage.
Example:
Derocheilocaris.
Subclass V. Copepoda:
1. Free or parasitic crustaceans found both in fresh and salt water.
2. Small bodied crustaceans; body segmented, divisible into head, thorax and abdomen.
3. Thoracic appendages typically biramous except the first which is uniramous.
4. Abdomen without appendages but provided with a pair of caudal styles.
5. Compound eyes absent but a single median eye present.
6. Antennules and antennae are usually well developed, mandibles usually with a palp.
7. Eggs are carried in egg sac (s) by females and larva is nauplius.
Order 1. Calanoida:
1. Found in freshwater lakes, ponds and also in sea water.
2. Body constricted just behind the segment bearing fifth leg.
3. Antennae biramous.
Examples:
Calanus, Diaptomus.
Order 2. Harpacticoida:
1. Found in freshwater, salt water and brackish water.
2. Body constriction scarce between segments bearing fourth and fifth legs.
3. Antennae biramous.
Example:
Harpacticus.
Order 3. Cyclopoida:
1. Found in freshwater lakes and ponds and also in salt water.
2. Body constriction between segments bearing fourth and fifth legs clearly apparent.
3. Antennae uniramous.
Example:
Cyclops.
Order 4. Monstrilloida:
1. Larvae parasitic in marine polychaete worms.
2. Mouth parts and antennae not found.
Example:
Monstrilla.
Order 5. Caligoida:
1. Ectoparasitic forms on freshwater and marine fishes.
2. Body articulation between third and fourth thoracic segments apparent in males.
3. Ectoparasites in gill-chambers of fishes.
4. Attachment to host body by antennae.
Example:
Caligus.
Order 6. Lernaeopodoida:
1. Ectoparasitic forms on freshwater and marine fishes.
2. Body segmentation not apparent.
3. Appendages reduced or none.
4. Usually attach to the host body by second maxillae.
Examples:
Lernaea, Salmincola.
Subclass VI. Branchiura:
1. Parasitic crustaceans living as ectoparasites on both freshwater and marine fishes.
2. Dorso-ventrally flattened body.
3. Carapace covers the cephalothorax.
4. Mouth suctorial.
5. Thoracic appendages five pairs.
6. Compound eyes present but sessile.
7. Abdomen small, un-segmented and bilobed.
8. Commonly called fish lice.
Example:
Argulus.
Subclass VII. Cirripedia:
1. Exclusively marine and sedentary forms.
2. Adults always fixed or may be parasitic.
3. Body segmentation poorly developed.
4. Carapace forms a pair of folds, the mantle which completely encloses the animal.
5. Compound eyes absent in adults.
6. Thoracic appendages six pairs and typically biramous.
7. Abdomen rudimentary usually having a pair of caudal styles.
8. Hermaphrodite (monoecious).
9. Commonly called barnacles.
Order 1. Thoracica:
1. Non-parasitic, sedentary forms.
2. Body surrounded by calcareous shell.
3. Thoracic limbs six pairs and biramous.
4. Alimentary canal present.
Examples:
Lepas (Goose barnacle), Balanus (Acorn barnacle).
Order 2. Acrothoracica:
1. Parasitic forms, bore into the shells of Mollusca and corals.
2. Body covered by large mantle.
3. Calcareous shell absent.
4. Thoracic appendages less than six pairs.
5. Alimenlary canal present.
Examples:
Alcippe, Cryptophialus.
Order 3. Ascothoracica:
1. Parasitic forms on Anthozoa and Echinodermata.
2. Thoracic appendages six pairs.
3. Mouth appendages are modified into piercing and sucking organs.
4. Alimentary canal mostly absent.
Examples:
Laura, Petrarca.
Order 4. Apoda:
1. Parasitic forms.
2. Body without mantle and thoracic appendages.
3. Body maggot-like.
4. Appendages and anus absent.
5. Hermaphrodite.
Example:
Proteolepas.
Order 5. Rhizocephala:
1. Parasitic forms on decapod crustraceans.
2. Body extremely degenerated.
3. Appendages and alimentary canal absent.
4. No trace of segmentation.
5. Attachment to host by a stalk with roots which penetrate into tissues of the host.
Example:
Sacculina.
Subclass VIII. Malacostraca:
1. Mostly large crustaceans found both in fresh and sea water.
2. Thorax comprises eight segments, while abdomen comprises six rarely seven segments.
3. Exoskeleton of head united with few or more thoracic segments to form cephalo- thoracic carapace.
4. Compound eyes are usually stalked.
5. Abdomen is devoid of caudal styles.
6. Development through zoaea stage; nauplius stage rarely occurs.
Order 1. Nebaliacea:
1. Primitive marine crustaceans.
2. Large bivalved carapace with an adductor muscle.
3. Thorax with eight pairs of leaf-like gills.
4. Abdomen contains seven segments and a telson.
5. Stalked eyes.
6. Telson with a pair of caudal style.
Example:
Nebalia.
Order 2. Mysidacea:
1. Marine crustaceans.
2. Carapace covers almost entire thorax.
3. Eyes stalked.
4. Thoracic appendages are all biramous.
5. Uropods form broad fan-like tail fin.
Examples:
Mysis, Hemimysis
Order 3. Isopoda:
1. Marine, freshwater, terrestrial or parasitic crustaceans.
2. Body dorso-ventrally flattened.
3. Carapace absent. Eyes sessile.
4. Abdomen is usually short.
Examples:
Oniscus, Bopyrus.
Order 4. Amphipoda:
1. Mostly marine crustaceans.
2. Body usually laterally compressed.
3. No carapace.
4. Eyes sessile.
5. Second and third pair of thoracic appendages are nearly always modified as prehensile organs.
Examples:
Caprella, Gammarus.
Order 5. Stomatopoda:
1. Marine forms.
2. Body elongated with broad abdomen.
3. Carapace small covering three thoracic segments.
4. Stalked eyes.
5. First five pairs of abdominal appendages are provided with gills.
6. Heart is elongated.
Example:
Squilla.
Order 6. Decapoda:
1. Mostly marine forms.
2. Carapace covers the entire thorax.
3. Thoracic appendages are modified as three pairs of maxillipedes and five pairs of walking legs.
4. Statocyst present.
Suborder:
1. Macrura:
Abdomen well developed, elongated and extended.
Antennules and antennae are both large.
Eyes are not enclosed in orbits.
Examples:
Palaemon, Astacus.
Suborder 2. Anomura:
1. Abdomen more or less reduced and fixed.
Examples:
Hippa, Eupagurus.
Suborder 3. Brachyura:
1. Abdomen is greatly reduced, hard and folded beneath the body.
Examples:
Cancer, Carcinus.
Class 2. Chilopoda:
1. Includes centipedes or hundred-leggers.
2. Body flattened dorso-ventrally and elongated.
3. Body divisible into head and trunk.
4. Head bears a pair of antennae, a pair of mandibles and a pair of maxillae.
5. Each trunk segment with a pair of legs.
6. First pair of legs modified to form poison claws.
7. Carnivorous, active and predaceous.
Order 1. Scutigeromorpha:
1. Legs 15 pairs and very long.
2. Much elongated antennae.
3. Spiracles unpaired, median and placed dorsally.
Example:
Scutigera.
Order 2. Lithobiomorpha:
1. Legs 15 pairs and very short.
2. Much elongated antennae having 19-70 segments.
3. Spiracles paired and placed laterally.
Example:
Lithobius.
Order 3. Geophilomorpha:
1. Burrowing forms having slender body.
2. Legs small, 31 to 170 pairs.
3. Spiracles paired and placed laterally.
4. Eyes absent and antennae possess 14 segments.
Example:
Geophilus.
Order 4. Scolopendromorpha:
1. Elongated body bears 21 or 23 pairs of legs.
2. Head with or without eyes, bears 17-30 jointed antennae.
3. Spiracles paired, placed laterally but in the anterior trunk segments.
Example:
Sclopendra.
Class 3. Symphyla:
1. Includes garden centipedes.
2. Terrestrial but found in damp places with humus.
3. Body divisible into head and trunk.
4. Head bears one pair of antennae one pair of mandibles and two pairs of maxillae.
5. Trunk 12-segmented, bearing one pair of legs in each segment.
6. Spiracles are present in head only; eyes absent.
7. Genital apertures are situated mid-ventrally between 4th pair of legs.
Examples:
Scutigerella, Scolopendrella.
Class 4. Pauropoda:
1. Minute, soft-bodied arthropods found in dark damp places usually under stones, logs, fallen leaves and in soil.
2. Body divisible into head and trunk.
3. Head bears a pair of antennae, a pair of mandibles and two pairs of maxillae forming lower lip.
4. Trunk bears 11 segments and anal pygidium.
5. Nine pairs of legs in trunk segments, eyes absent.
6. Gonopores lie mid-ventrally on 3rd segment.
Examples:
Pauropus, Decapauropus.
Class 5. Diplopoda:
1. Includes millipedes or thousand-leggers.
2. Body cylindrical, sub cylindrical, elongated and capable of being rolled up.
3. Body divisible into head, thorax and abdomen.
4. Head consists of five segments, thorax of four segments and abdomen of 20-100 segments.
5. Head possesses one pair of antennae, one pair of mandibles and one pair of maxillae.
6. Thoracic segments with one pair of legs in each, while abdominal segments bear two pairs of legs.
7. Poison claws not found.
8. Herbivorous in food habit.
9. Gonopores mid-ventrally situated on 3rd abdominal segment.
Order 1. Pselaphognatha:
1. Minute, body covered with serrated bristles.
2. Trunk bears 11 or 13 segments.
3. Gnathochilarium (fused maxillae of both the sides) with a pair of palps.
4. Integument soft.
5. Stink glands absent.
Examples:
Polyxenus, Lophoproctus.
Order 2. Pentazonia:
1. Body capable of being rolled up into a tight ball.
2. Trunk with 13-15 segments.
3. Each trunk segment with five sclerites.
4. One or two pairs of male gonopods, i.e., clasping organs present.
5. Stink glands not found.
Examples:
Glomeris, Onomeris.
Order 3. Nematomorpha:
1. Body segments 26 to 60; trunk segments 26 to 32.
2. Spinning glands two or three pairs.
3. Male gonopods one or two pairs on 7th segment.
4. Eyes present.
5. Commonly referred to as silk-spinning millipedes.
Examples:
Striaria, Cleidogono.
Order 4. Juliformia:
1. Trunk with 40 or more segments, commonly called snake millipedes.
2. Male gonopods one or two pairs on 7th segment.
3. Spinning glands not found.
4. Stink glands present on most of the trunk segments.
Examples:
Julus, Spirobolus.
Order 5. Colobognatha:
1. Trunk with 30 to 192 flattened segments commonly called suctorial millipedes.
2. Head conical and mouth parts small.
3. Male gonopods two pairs, one pair each in segments 7th and 8th.
4. Stink glands present.
Examples:
Polyzonium, Platydesmus.
Order 6. Polydesmoidea:
1. Trunk with 19 to 22 segments, commonly called flat-backed millipedes.
2. Male gonopods one or two pairs on 7th segments.
3. Spinning glands absent but stink glands present.
Examples:
Polydesmus, Oxidus.
Class 6. Insecta (L., insectum – being cut into):
1. Insects are air breathing mostly terrestrial and rarely aquatic arthropods.
2. Body is divided into three distinct regions head, thorax and abdomen.
3. Head consists of six fused segments and bears a pair of compound eyes, a pair of antennae and mouth parts adapted for chewing, biting, piercing, sucking, siphoning or sponging type.
4. Thorax comprises three free segments, each bearing a pair of legs and two pairs of wings borne on the second and third segments.
5. Abdomen comprises 7-11 segments and devoid of appendages.
6. Liver is absent but salivary glands are usually present.
7. Heart is elongated, tubular and is divided into eight chambers situated in the abdomen.
8. Respiration by branched tracheae.
9. Excretion by Malphigian tubules.
10. Sexes are separate.
11. Development is sometimes direct, more usually complicated by metamorphosis.
Subclass I. Apterygota (Gr., a = without ptera = wings):
1. Primitive wingless insects.
2. Metamorphosis is little or absent.
Order 1. Protura:
1. Minute soft bodied insects.
2. Antennae and compound eyes are absent.
3. Mouth parts are biting.
4. Abdomen twelve segmented.
5. Tracheae are absent.
6. Metamorphosis little.
Example:
Acerentomon.
Order 2. Thysanura:
1. Small primitive insects.
2. Body is elongated, flattened and naked or scaly.
3. Mouth parts biting; antennae long and well developed.
4. Abdomen eleven segmented.
5. A pair of cerci many segmented and a median caudal filament long.
6. Primitive metamorphosis.
Example:
Lepisma (Silver fish).
Order 3. Aptera:
1. Small, white or pale blind insects.
2. Body flattened.
3. Mouth parts biting.
4. Antennae long, many segmented.
5. Caudal filament absent.
6. Metamorphosis absent.
Example:
Campodea.
Order 4. Collembola:
1. Minute insects; body naked or covered with hair or scales.
2. Antennae four to six segmented.
3. Eyes absent.
4. Mouth parts biting,
5. Abdomen six segmented and usually with a ventral tube, tenaculum and spring.
6. Metamorphosis absent.
Examples: Spring tails, Snow flies.
Subclass II. Pterygota (Gr., ptera = wings):
1. Wings are usually present.
2. Abdomen devoid of appendages except genitalia and cerci.
3. Metamorphosis simple or complex.
Division I. Exopterygota:
1. Metamorphosis primitive or simple.
2. Young stages are nymphs.
3. Wings develop externally.
Order 5. Orthoptera:
1. Medium sized to large insects.
2. Usually with a pair of narrow leathery forewings or tegmina and a pair of well developed membranous hind wings.
3. Mouth parts strong biting and chewing.
4. Compound eyes and usually two or three ocelli.
5. Short or long, simple or segmented cerci.
6. Simple metamorphosis.
Examples:
Locusts, Grasshoppers Crickets, etc.
Order 6. Gryllobiattodea:
1. Small thysanuriform insects.
2. Wings absent, mouth parts biting type.
3. Antennae filiform, many segmented.
4. Compound eyes are small, ocelli absent.
5. Simple metamorphosis.
Example:
Grylloblatta.
Order 7. Blattaria:
1. Medium to large sized insects
2. Wings present or absent.
3. Antennae long, many segmented and filiform.
4. Mouth parts biting and chewing type.
5. Cerci prominent and segmented.
6. Metamorphosis simple.
Examples:
Periplaneta, Blatta.
Order 8. Phasmida:
1. Large leaf or stick-like insects.
2. Antennae usually long, filiform and may segmented.
3. Compound eyes are small, ocelli two or three or absent.
4. Mouth parts biting type.
5. Wings present or absent.
6. Cerci small and segmented.
Examples:
PhyIlium, Carausius (Stick insect).
Order 9. Mantodea:
1. Medium to large insects.
2. Head small, triangular and bears large compound eyes with three or more ocelli.
3. Mouth parts biting type.
4. Prothorax greatly elongated.
5. Fore-legs modified for capturing and holding the prey.
6. Wings large, small or absent. Metamorphosis is simple.
Example:
Mantis (Praying mantis).
Order 10. Dermaptera:
1. Small to medium sized insects.
2. Body is elongated with smooth or tough or chitinous covering.
3. Mouth parts biting type.
4. Abdomen is provided with force-like cerci at the posterior end.
5. Simple metamorphosis.
Example:
Forficula.
Order 11. Diploglossata:
1. Very small insects.
2. Body depressed covered with short hairs.
3. Mouth parts biting type.
4. Eyes and wings absent.
5. A pair of unsegmented cerci present.
6. Simple metamorphosis.
Example:
Hemimerus.
Order 12. Plecoptera:
1. Meidum to large sized, elongated somewhat flattened and soft bodied insects.
2. Head broad and bears a pair of long filiform 25 to 100 segmented antennae.
3. Compound eyes are moderate in size with two or three or no ocelli.
4. Mouth parts biting type.
5. Two pairs of equal many veined wings, hind pair with large anal area.
6. Abdomen eleven segmented, last segment reduced and bears long filiform multi-segmented cerci.
7. Simple or hemimetabolous metamorphosis.
8. Larvae are known as naiads which are aquatic.
Examples:
Stone flies, Salmon flies.
Order 13. Isoptera:
1. Social and polymorphic insects living in colonies under a caste system.
2. Small to medium sized mostly soft bodied and pale coloured insects.
3. Head small to very large, bears moniliform short or long many segmented antennae.
4. Mouth parts biting and chewing type.
5. Compound eyes vestigial with two or no ocelli.
6. Wings when present, two pairs, similar in size, shape and venation.
7. Cerci short and simple or 2-8 segmented.
8. Metamorphosis simple.
9. A colony contains both winged and wingless sexual individuals and wingless sterile workers and soldiers.
Examples:
Termites, White ants.
Order 14. Zoraptera:
1. Minute winged or wingless insects.
2. Antennae moniliform, nine segmented.
3. Compound eyes and ocelli are present in winged forms, absent in wingless forms.
4. Mouth parts biting type.
5. Cerci short and un-segmented.
6. Metamorphosis simple.
Example:
Zorotypus.
Order 15. Embioptera:
1. Small slender insects with somewhat flattened body.
2. Head large bears filiform antennae.
3. Compound eyes small in female, often large in male, ocelli absent.
4. Mouth parts biting chewing type.
5. Thorax nearly as long as abdomen.
6. First tarsal segment of fore-legs enlarged to contain glands and spinnerets.
7. Wings when present two pairs, membranous, similar in size and venation.
8. Metamorphosis simple or hemimetabolous.
Example:
Oligotoma.
Order 16. Corrodentia:
1. Small compact winged or wingless insects.
2. Head large and free, bears short or long filiform antennae.
3. Compound eyes are usually large or without ocelli.
4. Mouth parts modified biting type.
5. Cerci absent.
6. Metamorphosis simple.
Examples:
Book lice, Bark lice, Dust lice.
Order 17. Mallophaga:
1. Small wingless ectoparasitic insects.
2. Body is broad or elongated, flattened dorsally, tough and well chitinised.
3. Head hypognathus without setiform or clavate antennae.
4. Compound eyes are reduced, ocelli absent.
5. Mouth parts biting type.
6. Legs short with stout claws specialised for clasping hairs and feathers.
7. Cerci absent.
Example:
Bird lice.
Order 18. Anoplura:
1. Minute to small sized, permanently ectoparasitic on mammals.
2. Body is flattened, elongated without wings.
3. Head small with short 3-5 segmented, setiform antenne.
4. Compound eyes reduced or absent, ocelli absent.
5. Mouth parts piercing and sucking type.
6. Legs short with single claw specialised for grasping hairs.
7. Cerci absent.
Example:
Pediculus (Human louse).
Order 19. Ephemerida:
1. Small to medium sized, soft bodied delicate slender insects.
2. Antennae short setiform.
3. Mouth parts vestigial.
4. Well developed compound eyes and three ocelli present.
5. One or two pairs of fragile many veined wings.
6. Cerci are very long, filiform and multisegmented with a similar median caudal filament.
7. Metamorphosis simple or hemimetabolous.
8. Naiad (nymphs) are aquatic with abdominal tracheal gills.
Example:
Ephemera (May fly).
Order 20. Odonata:
1. Medium sized to large, slender, swift flying predaceous insects.
2. Head mobile, bears large compound eyes and ocelli.
3. Mouth parts biting type.
4. Two pairs of similar long narrow net- veined wings.
5. Naiads (nymphs) are aquatic with or without exterior gils.
6. Metamorphosis simple or hemimetabolous.
Examples:
Dragon flies, Damsel flies.
Order 21. Thysanoptera:
1. Minute, slender, terrestrial insects.
2. Body somewhat compressed dorsally or almost cylindrical.
3. Antennae short six to nine segmented.
4. Compound eyes with three ocelli present.
5. Mouth parts modified for piercing, chafing and sucking.
6. Wings when present two pairs of long and narrow with few veins.
7. Abdomen 10-11 segmented with an ovipositor.
8. Simple metamorphosis.
Example:
Thrips.
Order 22. Hemiptera:
1. Minute to large, oval or elongated and dorso-ventrally flattened terrestrial or aquatic insects.
2. Antennae 2 to 10 or rarely 25 segmented.
3. Eyes large with or without ocelli.
4. Mouth parts piercing and sucking type.
5. Wings when present two pairs, fore pair usually thickened basally and membranous apically in Heteroptera and wholly membranous in Homoptera.
6. Cerci absent.
7. Anal respiratory filaments present in some aquatic forms and anal filaments in male coccids.
8. Metamorphosis simple.
9. Mostly phytophagous, some are predaceous.
Examples:
Belostoma, Aphids, Cicadas, Scale insects.
Division II. Endopterygota:
1. Metamorphosis is complex (complete).
2. Young stages are known as larvae.
3. Wings develop internally.
Order 23. Megaloptera:
1. Medium to large sized insects.
2. Head prognathus, bears many segmented slender antennae.
3. Mouth parts biting type.
4. Wings two pairs, similar in shape, size and venation.
5. Cerci absent.
6. Metamorphosis complex including aquatic larvae.
Examples:
Sialis, Corydalus.
Order 24. Neuroptera:
1. Minute to medium sized, mostly terrestrial insects.
2. Head hypognathus, bears large and widely separated compound eyes.
3. Antennae usually filiform.
4. Mouth parts biting type.
5. Wings two pairs, similar in shape, size and venation.
6. Cerci absent.
7. Complex metamorphosis, carnivorous.
Example:
Chrysopa.
Order 25. Raphidiodea:
1. Small to medium sized, elongated, fragile terrestrial insects.
2. Antennae setiform, many segmented.
3. Compound eyes prominent with three or none ocelli.
4. Mouth parts biting type.
5. Two pairs of similar wings.
6. Female with long slender ovipositor.
7. Metamorphosis is complex.
Examples:
Snake flies, Serpent flies.
Order 26. Mecoptera:
1. Small to medium sized, slender, predaceous insects.
2. Head usually elongated and vertical.
3. Antennae long, filiform and many segmented.
4. Compound eyes are large and widely separated, ocelli three or none.
5. Mouth parts biting type.
6. Wings two pairs, similar in shape, size and venation.
7. Cerci short, simple or two segmented.
8. Metamorphosis complex.
Example:
Panorpa (Scorpion flies).
Order 27. Trichoptera:
1. Small to medium sized, diurnal and nocturnal moth-like insects.
2. Antennae long, filiform and many segmented.
3. Compound eyes are well developed with three or none ocelli.
4. Mouth parts biting type.
5. Wings two pairs, covered with hairs and scales.
6. Cerci one or two segmented.
7. Metamorphosis complex or holometabolic.
8. Larva aquatic.
Example:
Philopotamus (Caddis fly).
Order 28. Lepidoptera:
1. Medium to large sized flying terrestrial insects.
2. Body and wings are completely covered by flat overlapping, scales and hairs.
3. Antennae variable often clavate or serrate, hooked or knobbed or plumose.
4. Compound eyes large with two or no ocelli.
5. Mouth parts siphoning type with long coiled proboscis.
6. Wings two pairs, fore pair often largest.
7. Metamorphosis complex.
8. Larvae caterpillars with three pairs of thorcic legs and two to four pairs of abdominal prolegs.
Examples:
Butterflies, Moths.
Order 29. Coleoptera:
1. Minute to large insects with leathery integument.
2. Antennae variable in shape and size, usually 11 segmented.
3. Eyes conspicuous but cecelli absent.
4. Mouth parts biting and chewing type.
5. Wings two pairs, fore wings or elytra similar to body texture and useless in flight.
6. Abdomen usually 10 segmented.
7. Cerci absent.
8. Metamorphosis complex.
Examples:
Beetles, Weevils.
Order 30. Strepsiptera:
1. Minute free living and endoparasitic dimorphic insects.
2. Antennae short flabellate.
3. Eyes conspicuous but ocelli absent.
4. Mouth parts atrophied biting type.
5. Fore-wings small white, hind-wings large fan-shaped.
6. Metamorphosis complex and hyper metamorphosis.
Example:
Stylops.
Order 31. Hymenoptera:
1. Minute to large sised, social or parasitic insects
2. Antennae 12 segmented in male and 13 segmented in female.
3. Ocelli generally present.
4. Mouth parts sepcialised for biting, chewing lapping arid sucking.
5. Wings two pairs, membranous and narrow.
6. Abdomen always with basal pedicel.
7. Female with conspicuous ovipositor modified into saw, drill or sting.
8. Metamorphosis complex.
Examples:
Wasps, Bees, Ants.
Order 32. Diptera:
1. Minute to medium sized, diurnal, nocturnal, terrestrial and aquatic insects.
2. Body slender with fragile integument.
3. Antennae variable, simple or with arista.
4. Eyes large and separate with three ocelli.
5. Mouth parts modified for sucking, lapping piercing and sponging.
6. Fore-wings developed for flight, while- hind-wings reduced to halteres.
7. Metamorphosis complex.
8. Larvae limbless and vermiform known as maggots.
Examples:
Houseflies, Mosquitoes, Midges.
Order 33. Siphonoptera:
1. Minute to small sized insects ectoparasitic on birds and mammals.
2. Body laterally compressed.
3. Head small with or without eyes and ocelli.
4. Antennae short and capitate.
5. Mouth parts piercing and sucking type.
6. Cerci absent.
7. Metamorphoses complex.
Example:
Fleas.
