Phylum Arthropoda- Characteristics, classification, examples

Arthropoda (Arthropods) Definition

Arthropods are bilaterally symmetrical, triploblastic, metamerically segmented animals with coelom which is reduced and modified. Their body is covered externally in a chitinous exoskeleton which molts periodically and their appendages are joined.

Phylum Arthropoda Characteristics

  • They are bilaterally symmetrical, triploblastic, metamerically segmented animals.
  • Body organization is of an organ-system level.
  • The body is covered with a thick chitinous cuticle forming an exoskeleton.
  • Body segments usually bear lateral and jointed appendages with varied functions as jaws, gills, legs, etc.
  • Body divisible into head, thorax, and abdomen. Head and thorax often fused to form a cephalothorax.
  • The musculature is not continuous but comprises separate striped muscles capable of rapid contraction.
  • The body cavity is hemocoel. The true coelom is reduced to the spaces of the genital and excretory organs.
  • The complete digestive system with mouth and anus. Mouthparts adapted for various modes of feeding.
  • Open circulatory system with dorsal heart and arteries but without capillaries.
  • Respiration by general body surface, gills in aquatic forms, trachea, or book-lungs in terrestrial forms.
  • No true nephridia. Excretion organs are green glands or Malpighian tubules or coxal glands.
  • The nervous system is typically annelidan, with a dorsal brain connected with a nerve ring to a double ventral nerve cord.
  • Cilia are entirely absent from all parts of the body.
  • Sensory organs comprise eyes (simple and compound), chemo- and tactile receptors, balancing and auditory organs.
  • Sexes usually separate (dioecious). Reproduction organs and ducts paired.
  • Internal fertilization. Oviparous or ovoviviparous.
  • Development is usually indirect through larval stages. Parthenogenesis in some.
  • Parental care is often well marked in many arthropods.
  • Most diversified groups inhabiting the land, water, and air.

Read Also: Phylum Ctenophora- characteristics, classification, examples

Phylum Arthropoda
Created with BioRender.com

Phylum Arthropoda Classification

Phylum Arthropoda and its various groups have been classified differently by different workers. The classification here is followed by vandal (1949), snodgrass (1960), and strorer (1979). Onychophora is no longer consider as arthropods but consider as an independent group of segmented animals in modern trends.

Subphylum 1- Trilobitomorpha (Gr., tria=tree+ lobos=lobe+ morphe=form)

  • Represented by only fossil trilobites.
  • All marine forms.
  • All are bottom dwellers i.e. benthozoic and existed from Cambrian to Permian.
  • The body is three lobes separated by two longitudinal furrows.
  • Distinct head with one pair of antennae.
  • Except for the last segments, all bears biramous appendages.
  • Examples: Triarthrus, Dalmanites.

Subphylum 2- Chelicerata (Gr., chele=claw+ keros=horn+ ata=group)

  • Body divisible into anterior cephalothorax or prosoma and posterior abdomen or opisthosoma.
  • Prosomatic appendages 6 pairs. First pair of preoral chelicerae with claws with feeding in function.
  • The second pair of appendages are postoral pedipalpi and followed by 4 pairs of walking legs.
  • No antennae and true jaws.
  • Mostly terrestrial and predaceous.

Class 1. Merostomata (Gr., meros=thigh+ stoma= mouth)

  • Exclusively aquatic, all marine with median simple and lateral compound eyes.
  • 5 to 6 pairs of abdominal appendages modified as gills or branchiae for respiration.
  • Abdomen ending in a sharp telson or spine.
  • Excretion by coxal glands. No Malpighian tubules.

Subclass 1. Xiphosura (Gr., xiphos=sword+aura=tail)

  • Prosoma is convex covered by the abroad horseshoe-shaped carapace.
  • Prosoma bears 6 pairs of appendages.
  • Unsegmented abdomen with a long terminal telson.
  • Genital openings paired covered by a genital operculum.
  • Respiration is by lamelliform gills or book-gills attached to the abdominal appendages.
  • Example: Limulus (horseshoe or king crab).

Subclass 2. Eurypterida (Gr., eurys=broad+ pteryx=wing)

  • Extinct marine, giant water scorpions.
  • Large-sized arthropods.
  • Small cephalothorax covered by a dorsal carapace.
  • 12-segmented abdomen followed by cephalothorax which is narrow behind.
  • Cephalothorax with 6 pairs of appendages.
  • Examples: Eurypterus, Pterygotus.

Class 2. Arachnida (Gr., arachne=spider+ oid=like)

  • Terrestrial or aquatic forms.
  • Simple eyes. No compound eyes.
  • Prosoma bears 6 pairs of appendages; 1 pair of chelicerae, 1 pair of pedipalpi, and 4 pairs of walking legs.
  • No appendages in the abdomen.
  • Tracheae, book-lungs, or book-gills as a respiratory organ.
  • Excretion by coxal glands and Malpighian tubules.
  • Sexes separate (dioecious). mostly oviparous and courtship before mating.
  • Development direct.

Order 1. Scorpionida (=scorpiones)

  • Terrestrial forms found under stones in tropical and subtropical regions.
  • Elongated fair-shaped true scorpions.
  • Small prosoma broadly joined to large opisthosoma.
  • Prosoma covered dorsally by carapace and bears a pair of chelicerae, pair of pedipalpi, and 4 pairs of walking legs.
  • Opisthosoma divisible into broad anterior 7-segmented mesosoma and narrow posterior 5-segmented metasoma.
  • Metasoma ending in a telson and poison sting.
  • 2 ventral comb-like pectines on the 2nd abdominal segment.
  • Book-lungs as a respiratory organ.
  • Examples: Buthus, Palamnaeus, Androctonus.

Order 2. Pseudoscorpionida (=Chelonethida)

  • Tiny false scorpions.
  • Found under the bark of a tree.
  • Prosoma forms 6 fused segments covered dorsally by the carapace.
  • Abdomen 11-segmented, without sting and telson.
  • Chelicerae 2-jointed, with comb-like secretions.
  • Respiration by trachea.
  • Examples: Chelifer, Microcreagris.

Order 3. Palpigradi

  • Small-sized micro whip scorpions.
  • No eyes.
  • Prosomal carapace made of large anterior and smaller posterior portions.
  • Opisthosoma of 10-segments and jointed to prosoma by a pedicle.
  • Telson with the along jointed flagellum.
  • Chelicerae are chelate and pedipalpi leg-like.
  • 3 pairs of book-lungs as respiratory organs.
  • Example: Koenenia.

Order 4. Solifugae (=solifugida)

  • False spiders. Commonly called sun spiders or wind spiders.
  • The body consists of prosoma and opisthosoma.
  • Prosoma divided into a large anterior and a small posterior part.
  • Opisthosoma of 10 or 11 segments. No spinnerets.
  • Chelicerae large and chelate, pedipalpi are elongated and leg-like.
  • No poison glands.
  • Respiration by trachea.
  • A flagellum on each chelicera of male, for sperm transfer.
  • Example: Galedodes.

Order 5. Amblypygi (= Phrynichida)

  • Flattened scorpion-spiders or taillers whip scorpions.
  • Undivided carapace. Large and rhaptorial pedipalps.
  • Moderate size chelicerae.
  • 12-segmented abdomen without flagellum.
  • First pair of walking legs long, whip-like sensory in nature.
  • Example: Charinus.

Order 6. Uropygi (=pedipalpi)

  • Commonly referred to as a whip scorpion.
  • Consist of a pair of eyes.
  • Prosomal carapace entire.
  • Chelicerae 2-jointed and moderate in size.
  • Large, heavy, and usually with terminal pincers pedipalpi.
  • 12-segmented opisthosoma. Last segment with a long flagellum or telson.
  • Examples: Thelyphonus, Mastigoproctus.

Order 7. Araneae

  • True spiders.
  • The body consists of prosoma and opisthosoma.
  • Prosoma and opisthosoma without visible segments and jointed by a narrow pedicle.
  • Prosoma bears 6-pairs appendages.
  • Chelicerae 2-jointed, with a poison duct in terminal claw.
  • Simple leg-like pedipalps used for a transfer of sperms in males.
  • Opisthosoma with 3 pairs of spinnerets. No telson.
  • 8 eyes are arranged dorsally in 2 rows on the carapace of the prosoma.
  • Respiration by book-lungs or trachea or both.
  • Examples: Argiope (writing spider), Aranea (house spider), Lycosa (wolf spider), Agelena (funnel-web spider).

Order 8. Ricinulei (=Podogna)

  • Rare, small, tick-like, heavy-bodied arachnids.
  • The body consists of prosoma and opisthosoma.
  • Prosoma with an anterior hood-like movable plate (Cucullus).
  • Opisthosoma 9 segments and connected to prosoma by a pedicle.
  • Chelicerae and pedipalpi are chelate.
  • The third pair of legs in males form copulatory organs.
  • Respiration by trachea.
  • Examples: Cryptocellus, Ricinoides.

Order 9. Phalangida or Opiliones

  • Spider-like Harvest-men, Harvest-spiders, or daddy longlegs.
  • Small oval body. Extremely long, slender legs.
  • Unsegmented prosoma, opisthosoma bears 10 segments.
  • Prosoma broadly jointed to opisthosoma.
  • No spinning glands.
  • Respiration by trachea.
  • Examples: Phalangium, Leiobunum.

Order 10. Acarina

  • Commonly referred to as ticks and mites.
  • Free-living or parasitic.
  • Small, oval, and unsegmented body in which prosoma is fused with opisthosoma.
  • Chelicerae and pedipalpi are small and associated with the mouthparts which are adapted for biting, piercing, and sucking.
  • Respiratory organs trachea or skin.
  • Examples: Chorioptes (Mites), Sarcoptes (Itch-mite), Idodex (Tick).

Class 3. Pycnogonida

  • Commonly referred to as sea spiders.
  • Very small in size.
  • The body mainly consists of the cephalothorax, abdomen reduced.
  • Short segmented pedipalpi and very small chelicerae.
  • Usually 8 pairs of long walking legs.
  • Mouth placed on the long proboscis.
  • Simple eyes and 4 in numbers.
  • No respiratory or excretory organs.
  • Sexes separate (Dioecious). Females with a pair of ovigers for carrying eggs.
  • Examples: Pycnogonum, Nymphon.

Subphylum 3- Mandibulata (L., mandibula=mandible+ ata=group)

  • Terrestrial and aquatic both freshwater and marine.
  • Body divisible into either cephalothorax and abdomen or head, thorax, and abdomen.
  • Head appendages consist of 1 or two pairs of antennae, 1 pair of mandibles, and 1 or 2 pairs of maxillae.
  • Usually compound eyes.
  • Respiration by either gills or tracheae.
  • Malpighian tubules or green glands as excretory system.
  • Sexes separate with sexual dimorphism.
  • Development involves larval stages.

Class 1. Crustacea (L., crusta= a hard shell)

  • Mostly aquatic, generally marine but few freshwater and few live-in moist places.
  • Generally free-living but few are parasitic forms.
  • Head often joined with thorax to form cephalothorax covered dorsally by the carapace.
  • Chitinous, hard, limy exoskeleton.
  • 5-segmented head, bearing 2 pairs of antennae, 1 pair of mandibles, and 2 pairs of maxillae.
  • Typically, biramous appendages.
  • Respiration either by gills or general body surface.
  • Reduced coelom, is in the form of the hemocoel.
  • The blood vascular system comprises a dorsal contractile heart communicating by valvular Ostia with an enclosing pericardial sinus.
  • Excretion by either maxillary glands or antennary (green) glands.
  • Usually separate Sexual dimorphism is common.
  • Development with a nauplius stage.

Subclass 1. Cephalocarida

  • Body divisible into a horse-shoe shaped head and 19 segments trunk.
  • Only anterior 9 trunk bears appendages that appear triramous.
  • No eyes and carapace.
  • Head bears 2 pairs of antennae, a pair of jaws, and 2 pairs of maxillae.
  • Genital openings on the 19th segment.
  • Marine and bottom dweller forms.
  • Example: Hutchinsoniella.

Subclass 2. Branchiopoda

  • Freshwater, free-living, small-sized, primitive form.
  • Either-shield-like, bivalved shell-like, or even absent carapace.
  • Flattened, lobed, and leaf-like thoracic appendages provided with bristles.
  • Appendages serve for respiration (gills), locomotion, and filter-feeding.
  • No appendages in the stomach but bears a pair of caudal styles.
  • Antennules and 2nd maxillae reduced or absent.
  • Very common parthenogenesis.
  • The larva is nauplius.

Order 1. Anostraca

  • Commonly called fairy shrimps with 19 or more trunk segments.
  • Only anterior 11 to 19 segments.
  • Elongated body. Not well-developed carapace.
  • Stalked eyes.
  • Uniramous antennae.
  • Caudal stylets unjointed.
  • Examples: Branchipus, Artemia, Eubranchipus.

Order 2. Notostraca

  • Elongated body, carapace broad shield-shaped.
  • Sessile eyes (without a stalk).
  • Antennae reduced, anterior half with 35 to 71 pairs of appendages.
  • Caudal stylets many jointed.
  • Commonly called tadpole shrimps.
  • Examples: Apus, Lepidurus.

Order 3. Diplostraca

  • Laterally compressed body.
  • Usually transparent bivalved carapace enclosing body with or without the head.
  • Sessile eyes and usually united together.
  • Biramous, large antennae which are used for swimming.
  • Unjointed, curved, claw-like caudal style.
  • Commonly called clam-shrimps or water-fleas.
  • Examples: Daphnia, Limentis.

Subclass 3. Ostracoda

  • Small crustaceans found both in freshwater and sea.
  • Poorly segmented body entirely enclosed in a bivalved carapace.
  • 2 pairs of stout and cylindrical thoracic appendages.
  • Large antennules and antennae used for swimming.
  • Mandibles are provided with palps.
  • Common occurrences of parthenogenesis.
  • Commonly called a minute mussel or seed shrimps.

Order 1. Myodocopa

  • Found in seawater.
  • Carapace with antennal notches.
  • 2nd antennae biramous, enlarged at base.
  • 2nd antennae used in swimming.
  • Example: Cypridina.

Order 2. Podocopa

  • Both marine and freshwater forms.
  • Unnotched carapace without apertures for antennae.
  • 2 pairs of trunk appendages.
  • Uniramous 2nd antennae leg-like clawed at tips.
  • Examples: Cypris, Darwinula.

Order 3. Platycopa

  • Found in seawater.
  • Unnotched carapace without apertures for antennae.
  • 2nd antennae uniramous.
  • 1 pair of trunk appendages.
  • Antennae not used for swimming.
  • Example: Cytherella.

Order 4. Cladocopa

  • Found in seawater.
  • Unnotched carapace without apertures for antennae.
  • 2nd antennae biramous.
  • Both pairs of antennae used for swimming.
  • Example: Polycope.

Subclass 4. Mystacocarida

  • Small-sized crustaceans with elongated body divisible into the head, 5 -segmented thorax, and 6-segmented abdomen.
  • Well-developed head appendages also are the 1st thoracic pair (Maxillipedes).
  • Prominent antennules and antennae.
  • A single median eye. No compound eyes.
  • Limbless abdomen.
  • A pair of caudal stylets.
  • Sexes separate.
  • Metanauplius is the earliest known larval stage.
  • Example: Derocheilocaris.

Subclass 5. Copepoda

  • Free or parasitic crustaceans found both in fresh and saltwater.
  • Small body, segmented, divisible into the head, thorax, and abdomen.
  • Carapace absent.
  • Thoracic appendages typically biramous except 1st which is uniramous.
  • Limbless abdomen. Telson with 2 caudal styles.
  • No compound eyes but a single median eye present.
  • Long antennules. Small antennae.
  • Mandibles usually with a palp.
  • Eggs are carried in egg sac(s) by females.
  • The larva is nauplius.

Order 1. Calanoida

  • Found in freshwater lakes, ponds, and in seawater.
  • Body constricted just behind the segment bearing 5th leg.
  • Biramous antennae.
  • Examples: Calanus, Diaptomus.

Order 2. Harpacticoida

  • Found in freshwater, seawater, and brackish water.
  • Body constriction scarce between segments bearing 4th and 5th legs.
  • Biramous antennae.
  • Example: Harpacticus.

Order 3. Cyclopoida

  • Found in freshwater lakes and ponds and in saltwater.
  • Body constriction between segments bearing 4yh and 5th legs clearly apparent.
  • Uniramous antennae.
  • Example: Cyclops.

Order 4. Monstrilloida

  • Larvae parasitic in marine polychaete worms.
  • No mouthparts and antennae.
  • Example: Monstrilla.

Order 5. Caligoida

  • Ectoparasitic forms on freshwater and marine fishes.
  • Body articulation between 3rd and 4th thoracic segments apparent in males.
  • Ectoparasitic in gill-chambers of fishes.
  • Attached to the host body by antennae.
  • Example: Caligus.

Order 6. Lernaeopodoida

  • Ectoparasitic forms on freshwater and marine fishes.
  • Not apparent body segmentation.
  • Reduced or no appendages.
  • Usually attached to the host body by 2nd maxillae.
  • Examples: Lernaea, Salmincola.

Subclass 6. Branchiura

  • Commonly known as fish lice.
  • Parasitic crustaceans living as ectoparasites on the skin and gills chambers of fishes and some amphibians.
  • Dorso-ventrally flattened body.
  • Carapace shield-like which covers head and thorax.
  • Suctorial mouth.
  • Sessile compound eyes 1 pair.
  • No antennae and antennules.
  • 5 pairs of thoracic appendages.
  • 1st maxillae modified into suckers.
  • Unsegmented, bilobed abdomen.
  • Caudal claws minute.
  • Examples: Argulus, Dolops.

Subclass 7. Cirripedia

  • Exclusively marine and sedentary forms.
  • Commonly called barnacles.
  • Adults sessile, attached, or parasitic.
  • Poorly developed body segmentation.
  • Carapace forms a pair of folds of mantle surrounding the body and covered externally by calcareous plates.
  • No compound eyes and antennae in adults.
  • 6 pairs of thoracic appendages are typically biramous and cirriform.
  • The rudimentary abdomen usually having a pair of caudal styles.
  • Antennules become cement glands for attachment.
  • Hermaphrodites (monoecious).
  • Nauplius larva passes through cypris stages.

Order 1. Thoracica

  • Non- parasitic sedentary forms.
  • With or without a stalk, hermaphrodites.
  • Body surrounded a calcareous shell.
  • 6 pairs of thoracic appendages, cirriform.
  • Alimentary canal present.
  • Examples: Lepas (Goose barnacle), Balanus (Acorn barnacle).

Order 2. Acrothoracica

  • Parasitic forms bore into the shell of Mollusca and corals.
  • Unisexual.
  • Sessile.
  • Mantle reduced to a chitinous attachment disc.
  • A calcareous shell is absent.
  • Less than 6 pairs of thoracic appendages, cirriform.
  • Alimentary canal present.
  • Examples: Alcippe, Cryptophialus.

Order 3. Ascothoracica

  • Parasitic forms on Anthozoa as Echinodermata.
  • Bivalved or saccular mantle.
  • 6 pairs of thoracic appendages.
  • Mouth appendages are modified into the piercing and sucking organs.
  • No alimentary canal.
  • Examples: Laura, Petrarca.

 Order 4. Apoda

  • Parasitic forms.
  • No mantle and appendages.
  • Maggot-like body.
  • No anus.
  • Hermaphrodites.
  • Example: Proteolepas.

Order 5. Rhizocephala

  • Parasitic forms on decapod crustaceans.
  • Extremely degenerated body.
  • No appendages and alimentary canals.
  • No trace of segmentation.
  • Peduncle forms root-like absorptive branches ramifying throughout the host’s tissues.
  • Example: Sacculina.

Subclass 8. Malacostraca

  • Large crustaceans.
  • Found in fresh and seawater.
  • Typically made of 19 segments.
  • Head and one or more thoracic segments form a cephalothorax.
  • Thorax comprises 8 segments, while abdomen comprises 6 rarely 7 segments.
  • Well-formed or vestigial or no carapace.
  • Paired compound eyes are usually stalked.
  • The abdomen ends in a telson. No caudal styles.
  • Development through Zoaea stages; nauplius stages rarely occurs.

Order 1. Nebaliacea

  • Primitive marine crustaceans.
  • Bivalved carapace with an adductor muscle.
  • 8 pairs of leaf-like gills thorax.
  • 7 segments abdomen instead of 6 and a telson.
  • Staked eyes.
  • Telson with a pair of caudal style.
  • Example: Nebalia.

Order 2. Mysidacea

  • Marine crustaceans.
  • Elongated body.
  • Thin carapace covered almost the entire thorax.
  • Stalked eyes.
  • All biramous thoracic appendages.
  • Uropods form the broad fan-like tail fin.
  • Examples: Mysis, Hemimysis.

Order 3. Isopoda

  • Marine, freshwater, terrestrial or parasitic crustaceans.
  • Dorso-ventrally flattened body.
  • Head and 1 or 2 thoracic segments form a cephalothorax.
  • No carapace. Sessile eyes.
  • Usually short abdomen.
  • Commonly called woodlice.
  • Examples: Oniscus, Bopyrus.

Order 4. Amphipoda

  • Mostly marine crustaceans.
  • Laterally compressed body.
  • No carapace. Gills thoracic.
  • Sessile, lateral eyes.
  • Commonly referred to as sandhoppers.
  • Examples: Caprella, Gammarus.

Order 5. Stomatopoda

  • Marine forms.
  • Flattened body.
  • Small carapace covering 3 thoracic segments.
  • Large and broader abdomen than cephalothorax.
  • Staked eyes.
  • The First 5 pairs of abdomen appendages are provided with gills.
  • Elongated heart.
  • 2nd Maxillipedes raptorial.
  • Commonly called mantis shrimps.
  • Example: squilla.

Order 6. Decapoda

  • Mostly marine forms.
  • Well-developed carapace covering entire thorax.
  • The First 3 pairs of thoracic limbs form Maxillipedes and the remaining 5 pairs as walking legs.
  • Gills usually in 3 series present on the thorax.
  • Statocyst present.
  • Larva typically a Zoaea.

Suborder 1. Macrura

  • Well developed, elongated, and extended abdomen.
  • Both antennules and antennae are large.
  • Eyes are not enclosed in orbits.
  • Examples: Palaemon, Astacus.

Suborder 2. Anomura

  • Reduced or fixed abdomen.
  • Examples: Hippa, Eupagurus.

Suborder 3. Brachyura

  • Greatly reduced hard and folded abdomen beneath the body.
  • Examples: Cancer, Carcinus.

Class 2. Chilipoda (Gr., cheilos=lip+ pous=foot)

  • Includes centipedes or 100-leggers.
  • Dorso-ventrally flattened body and divisible into head and 15 to 173 trunk segments.
  • Head bears a pair of antennae, a pair of mandibles, and a pair of maxillae.
  • Legs 1 pair on each trunk segment.
  • 1st pair of legs form poison claws.
  • Carnivorous, active predaceous.

Order 1. Scutigeromorpha

  • 15 pairs of legs and very long.
  • Elongated antennae.
  • Unpaired, median, and dorsally placed spiracles.
  • Example: Scutigera.

Order 2. Lithobiomorpha

  • 15 pairs of legs and very short.
  • Many elongated antennae having 19-70 segments.
  • Paired and laterally placed spiracles.
  • Example: Lithobius.

Order 3. Geophilomorpha

  • Burrowing forms having slender bodies.
  • Small legs, 31 to 170 pairs.
  • Paired and laterally placed spiracles.
  • No eyes and antennae possess 14 segments.
  • Example: Geophilus.

Order 4. Scolopendromorpha

  • Body elongated bears 21 to 23 pairs of legs.
  • Head with or without eyes, bears 17-30 jointed antennae.
  • Paired, laterally placed spiracles, bout only in the anterior trunk segments.
  • Example: Scolopendra.

Class 3.  Symphyla (Gr., syn=together+ phylon= tribe)

  • Includes garden centipedes.
  • Terrestrial but found in damp places with hummus.
  • Slender body divisible into head and 15-22 trunk with 10-12 pairs of legs.
  • No eyes.
  • Head bears 1 pair of antennae, 1 pair of mandibles, and 2 pairs of maxillae.
  • Spiracles present in the head only.
  • Genital apertures are situated mid-ventrally between 4th pairs of legs.
  • Examples: Scutigerella, Scolopendrella.

Class 4. Pauropoda (Gr., pauros=small + Pous=foot)

  • Minute grub-like body divisible into head and 11-12 trunk segments with 9- 10 pairs of legs.
  • Soft-bodied arthropods found in dark damp places usually under stones, logs, fallen leaves and in soil.
  • Head bears a pair of antennae, a pair of mandibles, and 2 pairs of maxillae forming lower lip.
  • No eyes.
  • Gonopores lie mid-ventrally on 3rd segment.
  • Examples: Pauropus, Decapauropus.

Class 5. Diplopoda (Gr., diplos=double+ pous= foot)

  • Includes millipedes or thousand -leggers.
  • Elongated, cylindrical, sub-cylindrical, and capable of being rolled up the body.
  • Body divisible into the head, thorax, and abdomen.
  • 5-segmented head, 4-segmented thorax, and 20-100-segmented abdomen.
  • Head posses 1 pair of antennae, 1 pair of mandibles and 1 pair of maxillae.
  • Thoracic segments with 1 pair of legs.
  • Legs 2 pairs on each abdominal segment (Diplopoda).
  • No poison claws.
  • Herbivorous in food habit.
  • Mid-ventrally situated gonopores on 3rd abdominal segment.

Order 1. Pselaphognatha

  • Minute, body covered with serrated bristles.
  • 11 or 13 segments trunk.
  • Gnathochilarium (fused maxillae of both sides) with a pair of palps.
  • Soft integuments.
  • No stink glands.
  • Examples: Polyxenus, Lophoproctus.

Order 2. Pentazonia

  • Body capable of rolled up into a tight ball.
  • 13-15segments trunk.
  • Each trunk segment with 5 sclerites.
  • Male gonopods 1 or 2 pars i.e., clasping organs present.
  • No stink glands.
  • Examples: Glomeris, Onomeris.

Order 3. Nematomorpha

  • Body segments 26 to 60; trunk segments 26 to 32
  • 2 or 3 pairs of spinning glands.
  • 1 or 2 pairs of male gonopods on the 7th segment.
  • Eyes present.
  • Commonly referred to as silk-spinning millipedes.
  • Examples: Striaria, Cleidogono.

Order 4. Juliformia

  • Trunk with 40 or more segments commonly called snake millipedes.
  • 1 or 2 pairs of male gonopods on the 7th segment.
  • No spinning glands.
  • Stink glands present on most of the trunk segments.
  • Examples: Julus, Spirobolus.

Order 5. Colobognatha

  • Trunk with 30 to 192 flattened segments commonly called suctorial millipedes.
  • Conical head ad small mouthparts.
  • 2 pairs of male gonopods, 1 pair each in segments 7th and 8th.
  • Stink glands present.
  • Examples: Polyzonium, Platydesmus.

Order 6. Polydesmoidea

  • Trunk with 19 to 22 segments, commonly called flat-backed millipedes.
  • 1 or 2 pairs of male gonopods on 7th segments.
  • No spinning glands but stink glands present.
  • Examples: Polydesmus, Oxidus.

Class 6. Insecta (L., insectum=being cut into)

  • They are air-breathing mostly terrestrial and rarely aquatic arthropods.
  • Body made of the head (6 fused segments), thorax (3 segments), and abdomen (up to 11 segments).
  • Head bears a compound eye, a pair of antennae, and mouthparts adapted for chewing, biting, piercing, sucking, siphoning, or sponging type.
  • Thorax with 3 pairs of jointed legs and 1 or 2 pairs of wings which may be absent.
  • The abdomen is devoid of appendages.
  • No liver but salivary glands are usually present.
  • Elongated, tubular heart and id divided into 8 chambers situated in the abdomen.
  • Respiration by branched trachea.
  • Excretion by Malpighian tubules.
  • Unisexual.
  • Fertilization internal.
  • Development is sometimes direct, more usually complicated by metamorphosis.

Subclass 1. Apterygota (Ametabola) (Gr., a=without ptera=wings)

  • Primitive insects without wings.
  • Abdomen with cerci and style-like appendages.
  • Metamorphosis is little or absent.

Order 1. Protura

  • Minute soft-bodied insects.
  • No antennae and compound eyes.
  • No metamorphosis.
  • Mouthparts are biting.
  • 11segments abdomen plus a telson.
  • No trachea.
  • Example: Acerentomon.

Order 2. Thysanura

  • Small primitive insects.
  • Body covered by minute silvery scales.
  • Mouthparts biting: long antennae and well developed.
  • 11- segmented abdomen, Cerci, and telson long.
  • Primitive metamorphosis.
  • Example: Lepisma (Sliver fish).

Order 3. Aptera

  • Small, white, or pale blind insects.
  • Flattened body.
  • Mouth pats chewing.
  • Long, many segmented antennae.
  • No caudal filaments.
  • No metamorphosis.
  • Example: Campodea.

Order 4. Collembola

  • Minute insects; body naked or covered with hair or scales.
  • No eyes, trachea, Malpighian tubules, and metamorphosis.
  • Mouthparts chewing or sucking.
  • 4 to 6-segmented antennae.
  • 6-segmented abdomen and usually with a ventral tube, tenaculum, and spring.
  • Examples: Springtails, Snow flies.

Subclass 2. Pterygota (Metabola) (Gr., ptera=wings)

  • Wings present. Secondarily lost in some.
  • No abdominal appendages except cerci.
  • Simple or complex metamorphosis.

Division1. Exopterygota (Heterometabola)

  • Wings develop externally as buds.
  • Simple or primitive metamorphosis.
  • Young stages are nymphs.

Order 5. Orthoptera

  • Medium-sized or large insects.
  • 2 pairs of wings. Forewings or tegmina are straight and leathery. Hindwings membranous and folded at rest.
  • Mouthparts strong biting and chewing.
  • Large prothorax. Hindlegs jumping.
  • Compound eyes and usually 2 or 3 ocelli.
  • Short, long, simple, or segmented cerci.
  • Metamorphosis simple.
  • Examples: Locusts, Grasshoppers, Crickets, etc.

Order 6. Grylloblattodea

  • Small thysanuriform insects.
  • No wings.
  • Mouthparts biting types.
  • Filiform, may segmented antennae.
  • Small compound eyes, ocelli absent.
  • Metamorphosis simple.
  • Example: Grylloblatta.

Order 7. Blattaria

  • Medium to large-sized insects.
  • Wings present or absent.
  • Long, many segmented and filiform antennae.
  • Mouthparts biting and chewing type.
  • Prominent and segmented cerci.
  • Simple metamorphosis.
  • Examples: Periplaneta, Blatta.

Order 8. Phasmida

  • Large leaf or stick-like insects.
  • Usually long, filiform, and many segmented antennae.
  • Small compound eyes, ocelli 2 or 3 or absent.
  • Mouthparts biting type.
  • Wings present or absent.
  • Small and segmented cerci.
  • Examples: Phyllium, Carausius (Stick insect).

Order 9. Mantodea

  • Medium to large insects.
  • A small, triangular head bears large compound eyes with 3 or more ocelli.
  • Mouthparts biting types.
  • Greatly elongated prothorax.
  • Forelegs modified for capturing and holding the prey.
  • Large, small, or no wings.
  • Metamorphosis simple.
  • Example: Mantis (praying mantis).

Order 10. Dermaptera

  • Small to medium-sized insects.
  • Elongate body with smooth or tough or chitinous covering.
  • Mouthparts biting type.
  • The abdomen is provided with forceps-like cerci at the posterior end.
  • Metamorphosis simple.
  • Example: Forficula.

Order 11. Diploglossata

  • Very small insects.
  • Depressed body covered with short hairs.
  • Mouthparts biting types.
  • No eyes and wings.
  • A pair of segmented cerci present.
  • Metamorphosis simple.
  • Example: Hemimerus.

Order 12. Plecoptera

  • Medium to large-sized.
  • Elongated somewhat flattened and soft-bodied insects.
  • Broadhead bears a pair of long filiform 25 to 100 segmented antennae.
  • Moderate compound eyes with 2 or 3 or no ocelli.
  • Mouthparts biting type.
  • 2 pairs of equal many veined wings, hind pair with large anal area.
  • 11 segmented abdomen, the last segment reduced and bears long filiform multisegmented cerci.
  • Simple or hemimetabolous metamorphosis.
  • The aquatic larva is known as naiads.
  • Examples: Stoneflies, Salmon flies.

Order 13. Isoptera

  • Social and polymorphic insects living in colonies under a caste system.
  • Small to medium-sized mostly soft-bodied and pale-colored insects.
  • Small to very large head and bears moniliform short or long many segmented antennae.
  • Mouthparts biting or chewing types.
  • Vestigial compound eyes with 2 or no ocelli.
  • Wings 2 pairs when present, similar shape size, and venation.
  • Short and simple cerci or 2-8 segmented.
  • Simple metamorphosis.
  • A colony contains both winged and wingless sexual individuals and wingless sterile workers and soldiers.
  • Examples: Termites, white ants.

Order 14. Zoraptera

  • Minute wing or wingless insects.
  • Moniliform antennae with 9 segments.
  • Compound eyes and ocelli are present in winged forms, absent in wingless forms.
  • Mouthparts biting type.
  • Short and segmented cerci.
  • Simple metamorphosis.
  • Example: Zorotypus.

Order 15. Embioptera

  • Small slender insects with somewhat flattened bodies.
  • The large head bears a filiform antenna.
  • Small compound eyes in females, often large in males, no ocelli.
  • Mouthparts biting chewing types.
  • Thorax nearly as long as the abdomen.
  • 1st tarsal segment of forelegs enlarged to contain glands and spinnerets.
  • 2 pairs of wings when present, membranous, similar in size and venation.
  • Simple or hemimetabolous metamorphosis.
  • Example: Oligotoma.

Order 16. Corrodentia

  • Small compact winged or wingless insects.
  • The large and free head bears short or long filiform antennae.
  • Usually large compound eyes without ocelli.
  • Mouthparts modified biting types.
  • No cerci.
  • Simple metamorphosis.
  • Examples: Booklice, Bark lice, Dust lice.

Order 17. Mallophaga

  • Small wingless ectoparasitic insects.
  • Broad or elongated, dorsally flattened, tough, and well-chitinised body.
  • Head hypognathous without setiform or clavate antennae.
  • Reduced compound eyes, no ocelli.
  • Mouthparts biting type.
  • Short legs with stout claws specialized for clasping hairs and feathers.
  • No cerci.
  • Example: Bird lice.

Order 18. Anoplura

  • Minute to small-sized, permanently ectoparasitic on mammals.
  • Flattened, elongated body without wings.
  • Small with short 3-5 segmented setiform antennae on the head.
  • Reduced or no compound eyes, no ocelli.
  • Mouthparts piercing and sucking type.
  • Short legs with single claws specialized for grasping hairs.
  • No cerci.
  • Example: Pediculus (Human louse).

Order 19. Ephemerida

  • Small to medium-sized, soft-bodied delicate slender insects.
  • Short setiform antennae.
  • Mouthparts are vestigial.
  • Compound eyes wee-developed and 3 ocelli present.
  • 1 or 2 pairs of fragile many veined wings.
  • Very long, filiform and multisegmented cerci with a similar median caudal filament.
  • Simple or hemimetabolous metamorphosis.
  • Naiad (nymphs) are aquatic with abdominal tracheal gills.
  • Example: Ephemera (mayfly).

Order 20. Odonata

  • Medium-sized to large-sized, slender, swift flying predaceous insects.
  • The mobile head bears large compound eyes and ocelli.
  • Mouthparts biting type.
  • 2 pairs of similar long narrow net-veined wings.
  • Naiads(nymphs) are aquatic with or without exterior gills.
  • Simple or hemimetabolous metamorphosis.
  • Examples: Dragonflies, Damselflies.

Order 21. Thysanoptera

  • Minute, slender, terrestrial insects.
  • Somewhat dorsally compressed or almost cylindrical body.
  • Short 6 to 9 segmented antennae.
  • Compound eyes with 3 ocelli present.
  • Mouthparts modified for piercing, chafing, and sucking.
  • 2 pairs of wings long and narrow with few veins when present.
  • 10-11 segmented abdomen with an ovipositor.
  • Simple metamorphosis.
  • Example: Thrips.

Order 22. Hemiptera

  • Minute to large, oval or elongated, and dorso-ventrally flattened terrestrial or aquatic insects.
  • 2 to 10 or rarely 25 segmented antennae.
  • Large eyes with or without ocelli.
  • Mouthparts piercing and sucking type.
  • 2 pairs of wings when present, fore pair usually thickened basally and membranous apically in Heteroptera and wholly membranous in Homoptera.
  • No cerci.
  • Anal respiratory filaments present in some aquatic forms and anal filaments in male coccids.
  • Simple metamorphosis.
  • Mostly phytophagous, some are predaceous.
  • Examples: Belostoma, Aphids, Cicadas, scale insects.

Division 2. Endopterygota (Holometabolan)

  • Complex metamorphosis i.e. completes with larval and pupal stages.
  • Young stages are known as larvae.
  • Wings develop internally in pupal cases.

Order 23. Megaloptera

  • Medium to large-sized insects.
  • The prognathous head bears many segmented slender antennae.
  • Mouthparts biting type.
  • 2 pairs of wings, similar in shape, size, and venation.
  • No cerci.
  • Complex metamorphosis including aquatic larvae.
  • Examples: Sialis, Corydalus.

Order 24. Neuroptera

  • Minute to medium-sized, mostly terrestrial insects.
  • Head hypognathous, bears large and widely separated compound eyes.
  • Large wings, membranous, many- veined.
  • Long antennae usually filiform.
  • Mouthparts chewing type.
  • No cerci.
  • Larvae are carnivorous. Abdominal gills in aquatic larvae.
  • Complex metamorphosis.
  • Examples: Crysopa (Lacewing), Myrmeleon (Antlion).

Order 25. Raphidiodea

  • Small to medium-sized, elongated, fragile terrestrial insects.
  • Setiform, many segmented antennae.
  • Compound eyes prominent with 3 or more ocelli.
  • Mouthparts biting type.
  • 2 pairs of similar wings.
  • Female with a long slender ovipositor.
  • Complex metamorphosis.
  • Examples: snake flies, serpent flies.

Order 26. Mecoptera

  • Small to medium-sized, slender, predaceous insects.
  • Usually elongated and vertical head.
  • Long, filiform, and many segmented antennae.
  • Long, similar, narrow, membranous wings.
  • Large and widely separated compound eyes, ocelli 3 or none.
  • Mouthparts biting type, on a prolonged beak.
  • Short, simple, or 2 segmented cerci.
  • In males, the tip of the abdomen curved sting-like.
  • Complex metamorphosis.
  • Example: Panorpa (Scorpion flies).

Order 27. Trichoptera

  • Small to medium-sized, diurnal and nocturnal moth-like insects.
  • Long, filiform, and many segmented antennae.
  • Well developed compound eyes with 3 or none ocelli.
  • 2 pairs of wings long, hairy, folded roof-like over abdomens.
  • Mouth part biting type.
  • One or more segmented cerci.
  • Complex or holometabolic metamorphosis.
  • Larvae aquatic.
  • Example: Philopotamus (caddis fly).

Order 28. Lepidoptera

  • Medium to large-sized flying terrestrial insects.
  • Body and wings are completely covered by flat overlapping, scales, and hairs.
  • Antennae variable often clavate or serrate, hooked or knobbed or plumose.
  • Mouthparts sucking coiled under the head.
  • Large compound eyes with 2 or no ocelli.
  • 2 pairs of wings, the fore pair often largest.
  • Complex metamorphosis.
  • Larvae a caterpillar with 3 pairs of thoracic legs and 2 to 4 pairs of abdominal prolegs and chewing mouth.
  • Examples: Butterflies, Moths.

Order 29. Coleoptera

  • Minute to large insects with leathery integument.
  • Antennae variable in shape and size, usually 11 segmented.
  • Fore wings leathery (elytra). Hindwings membranous, folding.
  • Eyes conspicuous but ocelli absent.
  • Mouth part biting and chewing type.
  • Usually 10 segmented abdomens.
  • No cerci.
  • Complex metamorphosis.
  • Examples: Beetles, Weevils.

Order 30. Strepsiptera

  • Minute to free-living and endoparasitic dimorphic insects.
  • Short flabellate antennae.
  • Eyes conspicuous but ocelli absent.
  • Mouthparts atrophied biting type.
  • Small white fore-wings, large fan-shaped hind-wings.
  • Metamorphosis complex and hyper metamorphosis.
  • Example: Stylops.

Order 31. Hymenoptera

  • Minute to large-sized, social, or parasitic insects.
  • 12 segmented antennae in male and 13 in the female.
  • Ocelli generally present.
  • 2 pairs of wings, similar, membranous. On each side hooked together during flight.
  • Mouthparts specialized for biting, sucking, lapping, and chewing. Ovipositor of females usually forms a piercing sting.
  • Abdomen always with basal pedicel.
  • Complex metamorphosis.
  • Examples: Wasps, Bee, Ants.

Order 32. Diptera

  • Minute to medium-sized, diurnal, nocturnal, terrestrial, and aquatic insects.
  • Slender body with fragile integuments.
  • Antennae variable, simple or with arista.
  • Large and separate eyes with 3 ocelli.
  • Wings 1 pair. Fore-wings developed for flight and hind-wings as knob-like halters.
  • Mouthparts piercing-sucking or sponging.
  • Complex metamorphosis.
  • Larvae limbless and vermiform known as maggots.
  • Examples: Houseflies, Mosquitoes, Midges.

Order 33. Siphonoptera

  • Minute to small-sized insects ectoparasitic on birds and mammals.
  • Laterally compressed body. Secondarily wingless.
  • Small head with or without eyes and ocelli.
  • Short and capitate antennae.
  • Long and leaping legs.
  • Mouthparts piercing and sucking type.
  • No cerci.
  • Complex metamorphosis.
  • Examples: Pulex and Xenopsylla (Fleas).

References

  1. Kotpal RL. 2017. Modern Text Book of Zoology- Invertebrates. 11th Edition. Rastogi Publications.
  2. Jordan EL and Verma PS. 2018. Invertebrate Zoology. 14th Edition. S Chand Publishing.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.