Phylum Arthropoda Definition, Classification, Characteristics, Examples

Definition of Arthropoda (Arthropods)

The Arthropods belong to the bilaterally symmetrical, metamerically separated, triploblastic creatures with a coelom that is diminished and altered. Their body is externally covered in an exoskeleton made of chitin that is molted regularly as well as their appendages joined.

Characteristics of Phylum Arthropoda

These are bilaterally symmetrical, triploblastic, metamerically separated animals.
Body organization is on an organ system level.

The body is covered by thick chitinous cuticles, which form an exoskeleton.
Body segments generally have joints and lateral appendages that have different functions such as jaws, gills or legs, etc.
The body can be divided into the head the thorax, and the abdomen. Thorax and head often join to create an cephalothorax.

The musculature isn’t continuous but is composed of distinct muscles that are capable of rapid contraction.
The body cavity is hemocoel. The actual coelom has been reduced to the space of the excretory and genital organs.
The entire digestive system that includes the oral and anus. Mouthparts that can be adapted to different modes of eating.

A circulation system with dorsal and lateral arteries but with no capillaries.
Respiration is mediated by the general body surface or gills, for aquatic species, the trachea or book-lungs in terrestrial forms.
There is no true nephridia. Organs for excretion are green or Malpighian tubules, or coxal glands.

The nerve system is usually annelidan with an anterior brain linked by an annelidan nerve ring that connects to the ventral nerve cord.
Cilia are completely absent from the entire body.
Sensory organs include the eyes (simple or compound) as well as chemo- and tactile receptors, balance and auditory organs.

The sexes are usually separated (dioecious). Organs for reproduction and ducts that are paired.
Internal fertilization. Oviparous or Ovoviviparous.
Development usually occurs in indirect ways through the larval stage. Parthenogenesis is a possibility in certain species.

The importance of parental care is usually documented in a variety of arthropods.
The most diverse communities that reside on ground, water, and air.

Classification of Phylum Arthropoda

Phylum Arthropoda as well as its many categories have been classified in different ways by different researchers. The classification is closely followed by vandal (1949) and Snodgrass (1960) and also strorer (1979). Onychophora does not considered as arthropods but is seen as an autonomous animal group that is segmented according to the current fashions.

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

Only fossil trilobites are represented.
Marine forms in all their varieties.
All of us are inhabitants of the bottom i.e. benthozoic and lived since Cambrian up to Permian.

The body is composed of three lobes, separated by two furrows along the length of the body.
A distinct head that has only one antennae.
With the exception of the last segment that are biramous, the rest bear biramous appendages.

Examples: Triarthrus, Dalmanites.

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

Body divided into anterior cephalothorax, or prosoma and posterior abdomen, also known as opisthosoma.
Prosomatic appendages in 6 pairs. The first set of preoral chelicerae that have claws and feeding functions.

The other pair of appendages is postoral pedipalpi. They are then 4 sets of walking legs.
True jaws and no antennae.
Predaceous and terrestrial, mostly.

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

All marine, exclusively aquatic with medial simple and lateral compound eye.
5 to 6 pairs of abdominal appendages that have been modified to function as branchiae or gills for breathing.
Abdomen, which ends in a sharp telson , or spine.

Excessive excretion through coxal glands. No Malpighian tubules.

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

Prosoma is covered in convexity by the horseshoe-shaped outer carapace.
Prosoma is a sperm-based cell that has six Appendages in pairs.

Unsegmented abdomen, with an extended terminal telson.
Genital openings, paired and with an operculum genital.
Respiration is facilitated by lamelliform or book-gills that are attached to abdominal appendages.

Examples: Limulus (horseshoe or King crab).

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

Extinct marine, huge water scorpions.
Large-sized arthropods.

Small cephalothorax covered with an dorsal carapace.
Cephalothorax is a 12-segmented abdomen that is smaller in the back.
Cephalothorax with six pair of appendages.

Examples: Eurypterus, Pterygotus.

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

Forms of aquatic or terrestrial life.
Simple eyes. No compound eyes.

Prosoma has six pairs of appendages: one pair of chelicerae 1 pair of pedipalpi and four pair of legs for walking.
No abdominal appendages.
Tracheae, book-lungs or book-gills for an organ for breathing.

Excretion through coxal glands and Malpighian tubules.
Sexes separate (dioecious). typically oviparous, and courtship prior to mating.
Development direct.

Order 1. Scorpionida (=scorpiones)

Terrestrial forms that are under the surface of stones in subtropical and tropical areas.
Long-legged fair-shaped true scorpions.
Small prosoma, broadly linked to a large the opisthosoma.

Prosoma is covered dorsally with carapace. It is accompanied by two chelicerae, pedipalpi pair, as well as four walking legs.
Opisthosoma is divided into mesosoma that is broad and anterior, 7-segmented and narrow metasoma that is 5-segmented in the posterior.
Metasoma that ends in an elson and poison sting.

2 pectines that resemble combs on the 2 2nd abdominal segment.
Book-lungs as respiratory organs.
Examples: Buthus, Palamnaeus, Androctonus.

Order 2. Pseudoscorpionida (=Chelonethida)

Tiny fake scorpions.
It was found under the bark of an oak tree.
Prosoma is composed of 6 fused segments that are covered dorsally by the carapace.

Abdomen 11-segmented without the sting or telson.
Chelicerae 2jointed, with comb-like secretions.
Respiration through the trachea.

Examples: Chelifer, Microcreagris.

Order 3. Palpigradi

Micro-sized micro-sized scorpions with micro whip.
No eyes.

Prosomal carapace is composed of larger anterior and smaller lateral parts.
Opisthosoma with 10 segments joined to prosoma with the pedicle.
Telson with the joined flagellum.

Chelicerae include pedipalpi and chelate. leg-like.
Three pairs of book-lungs that function as respiratory organs.
Example: Koenenia.

Order 4. Solifugae (=solifugida)

False spiders. Often referred to as sun spiders and wind-spinning spiders.
The body is composed of prosoma and the opisthosoma.
Prosoma split into a large anterior and smaller posterior portion.

Opisthosoma comprised of between 10 and 11 segments. There are no spinnerets.
Chelicerae are large and chelate. pedipalpi have a leg-like shape and are elongated.
There are no poison glands.

The trachea is the main source of respiration.
A flagellum is located on each male chelicera, to facilitate the transfer of sperm.
Example: Galedodes.

Order 5. Amblypygi (= Phrynichida)

Smaller or flattened scorpion-spiders whip scorpions.
Carapace with a divided carapace. The pedipalps are large, and they rhaptorial.
Moderate size chelicerae.

12-segmented abdomen, without flagellum.
The first pair of walking legs long, like whips in the natural world.
Example: Charinus.

Order 6. Uropygi (=pedipalpi)

Sometimes referred to as whip scorpion.
Consists of a pair eyes.
Prosomal carapace, complete.

Chelicerae 2jointed and medium in size.
Heavy, large and typically with pincers on the terminals of pedipalpi.
12-segmented opisthosoma. The last segment has the long flagellum or Telson.

Examples: Thelyphonus, Mastigoproctus.

Order 7. Araneae

True spiders.
The body is composed of prosoma and the opisthosoma.

Prosoma and opisthosoma with no visible segments, joined by a pedicle that is narrow.
Prosoma bears appendages with 6 pairs.
Chelicerae 2jointed, with an apex of poison in the terminal claw.

Simple pedipalps that resemble legs that are used to transfer male sperms.
Opisthosoma with 3 spinnerets. There is no telephone.
8 eyes are laid out dorsally, in two rows in the prosoma’s carapace.

Book-lung or trachea-related respiratory tract 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 is made up of prosoma as well as the opisthosoma.
Prosoma that has an anterior hood-like removable plates (Cucullus).
Opisthosoma 9 segments , connected to prosoma via the pedicle.

Chelicerae and Pedipalpi are both Chelate.
The third set of legs in males are copulatory organs.
The trachea is the main source of respiration.

Examples: Cryptocellus, Ricinoides.

Order 9. Phalangida or Opiliones

Spider-like Harvest-men or Harvest-spiders and daddy-longlegs.
The body is small and oval. body. Extremely long, slender legs.

Unsegmented prosoma, opisthosoma bears 10 segments.
Prosoma is broadly joined to opisthosoma.
No spinning glands.

The trachea is the main source of respiration.
Examples: Phalangium, Leiobunum.

Order 10. Acarina

Commonly called ticks and mites.

The parasite or free-living.
Small, oval and non-segmented body where prosoma is fused to the opisthosoma.
Chelicerae and pedipalpi are both small and are connected to the mouthparts that are designed to piercing, biting and sucking.

Skin or trachea are respiratory organs.
Examples: Chorioptes (Mites), Sarcoptes (Itch-mite), Idodex (Tick).

Class 3. Pycnogonida

Sometimes known as sea spiders.

Very tiny in terms of size.
The body mostly consists of cephalothorax, abdominal reduced.
Pedipalpi with short segments and tiny Chelicerae.

Typically eight pairs of long walking legs.
Mouth placed on long proboscis.
Simple eyes and four in numbers.

There are no respiratory or excretory organs.
Sexes separate (Dioecious). Females sporting a pair of egg-carriers to carry eggs.
Examples: Pycnogonum, Nymphon.

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

Terrestrial and aqua, both sea and fresh water.
Body divided into either the cephalothorax and abdomen, or the head, thorax and abdomen.
Head appendages are comprised of 2 or more pairs of antennae, one mandible and one or two maxillae.

Usually, compound eyes.
The respiratory system is characterized by the tracheae or the gills.
Malpighian tubules, also known as green glands in the excretory system.

Sexual dimorphism is a way to distinguish genders.
Development involves larval stages.

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

Most of the time, it is marine, however there are a few freshwaters and a some live-in moist areas.

Most free-living, but a some parasite forms are.
The head is often joined to the thorax , forming a cephalothorax that is which is covered dorsally by the carapace.
Chitinous soft, hard exoskeleton, limy.

Five-segmented head with two antennae pairs one pair of mandibles and two maxillae.
Typically biramous appendages are common.
Inhalation, either through gills or the general body surface.
Reduced coelom is the form of hemocoel.
Blood vascular system includes a dorsal contractile heart, which communicates through the valvular Ostia, which is encircled by a the pericardial sinus.
Excretion is controlled by either the analyte or maxillary (green) glands.
In general, separate sexual dimorphism is typical.
Nauplius stage of development.

Subclass 1. Cephalocarida

The body is divided into a horse-shoe head shape and 19 segments trunk.
Only the anterior 9 trunk has appendages that look triramous.
Eyes and carapace are not present.
Head has two antennae, a pair jaws and two maxillae.
Genital openings are found on the 19 section. Genital openings are seen on the 19 segment.
Forms of bottom dweller and marine.
Example: Hutchinsoniella.

Subclass 2. Branchiopoda

Small-sized freshwater basic form.
It can be bivalved, shield-like, or even without a carapace.
Flattened leaves, lobed, and leaf-like appendages for the thoracic limbs, with bristles.
Appendages are used for breathing (gills) and locomotion and for filter-feeding.
There are no stomach appendages but it does have a pair caudal forms.
Antennules, and the 2 2nd maxillae diminished or absent.
Parthenogenesis very common.
The larva is called nauplius.

Order 1. Anostraca

Subclass 3. Ostracoda

Small crustaceans are found in freshwater and at sea.
Poorly segmented body completely covered in a bivalved carapace.
2 pairs of stout , and cylindrical appendages to the thorax.
Large antennae and antennules designed for swimming.
Mandibles are supplied with an e-syringe.
Commonly occurring manifestations of parthenogenesis.
Sometimes referred to as the minute mussel, or seed shrimps.

Order 1. Myodocopa

It was found in the seawater.
A carapace that has notches for antennas.
2 2nd antennae biramous. It is enlarged at the base.
2 2nd antennas used in swimming.
Example: Cypridina.

Order 2. Podocopa

Freshwater and marine.
Unnotched carapace with no apertures to allow antennae.
Two pair of appendages to the trunk.
Uniramous 2 2antennae claws that resemble legs at the ends.
Examples: Cypris, Darwinula.

Order 3. Platycopa

It was found in the seawater.
Unnotched carapace with no apertures to allow antennae.
2nd antennae uniramous.
1 . Two trunk appendages.
Antennae are not designed for swimming.
Example: Cytherella.

Order 4. Cladocopa

It was found in the seawater.
Carapace with no apertures, notched and without antennae.
2nd antennae biramous.
The antennae are used in pairs to swim.
Example: Polycope.

Subclass 4. Mystacocarida

Small-sized crustaceans, with an extended body that is divisible into the head, the thorax, five-segmented and a six-segmented abdominal.
The head appendages that are well developed constitute the one 1st Thoracic Pair (Maxillipedes).
Antennules with prominent antennules and antennae.
A single median eye. No compound eyes.
Limbless abdominal.
A pair of stylets for caudal.
The sexes are different.
Metanauplius is one of the earliest identified larval stage.
Example: Derocheilocaris.

Subclass 5. Copepoda

The crustaceans are parasitic or free, and can be can be found both in fresh and saltwater.
Small body that is segmented and split into chest, the thorax and the head. abdomen.
Carapace is absent.
Appendages to the thoracic artery are typically biramous, with the one st that is uniramous.
Limbless abdomen. Telson with two caudal styles.
There are no compound eyes present, only one median eye is present.
Long antennules. Small antennae.
Mandibles typically have a prick.
Eggs are carried around in eggs sac(s) from females.
The larva is known as nauplius.

Order 1. Calanoida

They are found in lake bodies, freshwater ponds as well as in seawater.
The body is constricted to the segment that bears 5 the leg.
Antennas of Biramous.
Examples: Calanus, Diaptomus.

Order 2. Harpacticoida

In freshwater, seawater, as well as brackish water.
The body constriction is minimal between segments with legs 4 4 as well as 5 5 legs.
Antennas with biramous.
Example: Harpacticus.

Order 3. Cyclopoida

It is found in freshwater lakes and ponds, as well as in saltwater.
The body constriction between segments that bear the 4yh as well as 5 the legs is evident.
Uniramous antennae.
Example: Cyclops.

Order 4. Monstrilloida

Larvae that are parasitic to marine polychaete Worms.
No antennae or mouthpieces.
Example: Monstrilla.

Order 5. Caligoida

Ectoparasitic forms found on marine and freshwater fishes.
Body joint between 3 3rd as well as 4 4 thoracic segments is evident in males.
Ectoparasitic is found in the gill chambers of fishes.
It is connected with the body via antennae.
Example: Caligus.

Order 6. Lernaeopodoida

Ectoparasitic forms of Marine and freshwater fishes.
Not apparent body segmentation.
Appendages that are not reduced or removed.
Usually , they are attached to the host body via 2 2 maxillae.
Examples: Lernaea, Salmincola.

Subclass 6. Branchiura

Often, it is referred to as fish lice.
Parasitic crustaceans that live as ectoparasites living on the gills and skin chambers of fishes as well as amphibians.
Dorsoventrally flattened body.
Carapace shield like that which covers the thorax and head.
Suctorial mouth.
Eyes Sessile Compound 1 Pair.
There are no antennae or antennules.
Five pairs of appendages to the thoracic area.
1 1 maxillae changed into suckers.
A stomach that is not segmented, and bilobed.
Caudal claws minute.
Examples: Argulus, Dolops.

Subclass 7. Cirripedia

Only marine and sedentary forms.
Often, they are referred to as barnacles.
Adults that are attached, sessile or parasitic.
Poorly designed body segmentation.
Carapace is a pair of mantle folds that surround the body and is covered on the outside by plates of calcareous.
No antennae or compound eyes in adults.
Six Appendages of the thoracic are usually Biramous as well as cirriform.
The abdomen is rudimentary, usually with two caudal styles.
Antennules are converted into cement glands to attach.
Hermaphrodites (monoecious).
Nauplius larva moves through cypris stage.

Order 1. Thoracica

Non-parasitic forms of sedentary.
Without or with an herbaphrodite stalk.
Body is enclosed by calcareous.
Six pairs of appendages for the thoracic, in cirriform.
The canal is a part of the alimentary tract.
Examples: Lepas (Goose barnacle), Balanus (Acorn barnacle).

Order 2. Acrothoracica

Parasitic forms penetrate the shells of Mollusca and corals.
Unisexual.
Sessile.
Mantle reduced to an attachment disc with chitinous material.
The shell of calcareous is not present.
Six pairs or less of appendages for the thoracic and cirriform.
The canal is a part of the alimentary tract.
Examples: Alcippe, Cryptophialus.

Order 3. Ascothoracica

Parasitic forms of Anthozoa such as Echinodermata.
Saccular or bivalved mantle.
Six pairs of appendages for the thoracic region.
The mouth appendages are transformed into sucking and piercing organs.
There is no alimentary canal.
Examples: Laura, Petrarca.

Order 4. Apoda

Parasitic forms.
There is no mantle or appendages.
Maggot-like body.
There is no Anus.
Hermaphrodites.
Example: Proteolepas.

Order 5. Rhizocephala

Parasitic forms of decapod crustaceans.
Degraded and severely deformed body.
There are no appendages or alimentary canals.
No evidence of segmentation.
The peduncle is a root-like branch which ramify through the tissues of the host.
Example: Sacculina.

Subclass 8. Malacostraca

Large crustaceans.
It is found in fresh and saltwater.
Usually made up of 19 sections.
The head and one or two thoracic segment create the cephalothorax.
Thorax has 8 segments while the abdomen is comprised of 6 times 7 segments.
Formally well-formed, vestigial or without carapace.
Compound eyes that are paired are generally stalked.
The abdomen is finished in an elongated the telson. No caudal styles.
The development process is via Zoaea stages; Nauplius stages seldom occur.

Order 1. Nebaliacea

Marine crustaceans that are primitive.
Bivalved carapace that has muscles of the adductor.
eight pairs of leaf-like, gills in the thorax.
7 segments abdominal in place of the 6 that is an elson.
Eyes piercing.
Telson wearing a pair of caudal-style.
Example: Nebalia.

Order 2. Mysidacea

Marine crustaceans.
Long body.
The carapace was thin and covered nearly the entire the thorax.
Eyes with a tangle.
All biramous appendages of the thoracic.
Uropods make up the tail fin that resembles a fan.
Examples: Mysis, Hemimysis.

Order 3. Isopoda

Freshwater, marine, terrestrial and parasitic crustaceans.
Dorsoventrally flattened body.
Head and one or two segments of thoracic make up the cephalothorax.
There is no carapace. Sessile eyes.
Most often, it is a short abdomen.
Commonly referred to as woodlice.
Examples: Oniscus, Bopyrus.

Order 4. Amphipoda

Most marine crustaceans.
The body is compressed laterally. body.
Carapace not present. Gills in the thoracic.
Sessile, lateral eye.
They are often called Sandhoppers.
Examples: Caprella, Gammarus.

Order 5. Stomatopoda

Marine forms.
Flattened body.
Small carapace that covers three thoracic segments.
The abdomen is larger and wider that cephalothorax.
Eyes that are stray.
The initial five abdominal appendages are equipped with gills.
Heart with a long neck.
2nd Maxillipedes raptorial.
Also known as mantis shrimps.
Example: squilla.

Order 6. Decapoda

The majority of marine forms.
A well-developed carapace that covers the entire thorax.
The first 3 pairs of thoracic legs form Maxillipedes while the rest of the five pairs function as walking legs.
Gills are usually 3 series that are located on the thorax.
Statocyst present.
The most common species of Larva is Zoaea.

Suborder 1. Macrura

Well-developed, elongated and an extended abdomen.
Antennules and antennae both are both large.
Eyes aren’t encased within orbits.
Examples: Palaemon, Astacus.

Suborder 2. Anomura

Fixed or reduced abdomen.
Examples: Hippa, Eupagurus.

Suborder 3. Brachyura

The body is incredibly soft and abdominal muscles folded under the body.
Examples: Cancer, Carcinus.

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

This includes centipedes as well as 100-leggers.
Flattened Dorso-ventrally body and divided between head as well as 15 to 173 trunk segments.
Head is a solitary body with a pair of antennae, a pair mandibles, as well as maxillae.
Legs 1 pair for every trunk section.
The first pair of legs are poison claws.
Carnivorous, active predaceous.

Order 1. Scutigeromorpha

15 pairs of legs , and extremely long.
Long-length antennae.
Median, unpaired, and dorsally located spiracles.
Example: Scutigera.

Order 2. Lithobiomorpha

15 legs in a row and extremely small.
Many antennas with elongated 19-70 segments.
Laterally and laterally placed spiracles.
Example: Lithobius.

Order 3. Geophilomorpha

Forms of burrowing with slim bodies.
Small legs Small legs, 31 to 170 pairs.
Laterally and laterally placed spiracles.
No antennas or eyes have 14 segments.
Example: Geophilus.

Order 4. Scolopendromorpha

Body elongated bears 21 – 23 legs.
Head without or with eyes It has 17-30 jointed antennae.
Laterally placed, paired spiracles that only affix in the trunk segment that is anterior.
Example: Scolopendra.

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

Includes garden centipedes.
Terrestrial, but often found in damp areas with Hummus.
A slim body divided into the head and 15-22 trunk, with 10-12 legs.
No eyes.
Head is adorned with one pair of antennae 1 mandible pair, and two maxillae.
The head contains a few spiracles only.
Genital apertures are located mid-ventrally between the 4th pair of legs.
Examples: Scutigerella, Scolopendrella.

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

Minute grubby body split in head segments and between 11-12 trunks. 9-10 legs.
Soft-bodied arthropods are found in dark , damp areas typically under logs, rocks as well as fallen leaves. They can also be found in soil.
Head is comprised of a pair antennae, two mandibles and two maxillae that form the lower lips.
No eyes.
Gonopores are located mid-ventrally on the 3rd segment.
Examples: Pauropus, Decapauropus.

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

Millipedes, or thousand-leggers.
Long, cylindrical, sub-cylindrical and capable of being rolled over the body.
The head is divisible into the abdomen stomach, thorax and head.
5-segmented head and thorax, four-segmented and 20-100-segmented abdominal.
Head has one pair of antennae, one mandible and one couple of maxillae.
Thoracic segments, with one set of legs.
Legs Two pairs of every abdominal section (Diplopoda).
No poison claws.
Food habits that are herbivores.
In the mid-ventral region, gonopores located on the third abdominal section.

Order 1. Pselaphognatha

Moment, body covered with serrated bristles.
1 or 13 trunk segments.
Gnathochilarium (fused maxillae on the two sides) with the palps of a pair.
Soft inguments.
No stink glands.
Examples: Polyxenus, Lophoproctus.

Order 2. Pentazonia

Body that can be wrapped into an elongated ball.
13-15segments trunk.
Each trunk segment has five sclerites.
Male Gonopods one or two pars i.e. organs that clasp that are present.
No stink glands.
Examples: Glomeris, Onomeris.

Order 3. Nematomorpha

The body segments from 26-60 and trunk segments 26 to 32
Two or three pair with spinning glands.
Two or more male gonopods in a pair within the seven 7segment.
Eyes present.
Often, they are known as silk-spinning millipedes.
Examples: Striaria, Cleidogono.

Order 4. Juliformia

Trunk made up of up to 40 segment is commonly known as snake millipedes.
One or two male gonopods in the seventh segment.
No spinning glands.
Stink glands are present on the majority parts of trunks.
Examples: Julus, Spirobolus.

Order 5. Colobognatha

Trunk that has 30 to 192 segments that are flattened often referred to as suctorial millipedes.
Conical head and small mouthpieces.
Two male gonopods. 1 pair for segments 7th and 8th segments.
Stink glands present.
Examples: Polyzonium, Platydesmus.

Order 6. Polydesmoidea

Trunk made up of 19-22 segments, often referred to as millipedes that have a flat-back.
One or two male gonopods in pairs on 7th segments.
There are no spinning glands. However, there are stink glands are present.
Examples: Polydesmus, Oxidus.

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

They breathe air mostly in terrestrial, but rarely aquatic arthropods.
The body is composed of the head (6 segmented fused) and Thorax (3 segments) and abdominal (up up to 11 sections).
Head is an eye that is compound and antennae, as well as mouthparts designed for biting, chewing, siphoning, piercing or sponging.
Thorax that has 3 pairs of joined legs and 1 or two pairs of wings that could be missing.
The abdomen is without appendages.
The salivary glands, which are not livers, are typically present.
A long, tubular heart that is divided into 8 chambers in the abdomen.
Respiration via a the branched Trachea.
Excretion through Malpighian tubules.
Unisexual.
Fertilization internal.
The process of development can be directly, but more often complex due to metamorphosis.

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

Primitive insects that don’t have wings.
Abdomen with style-like appendages and cerci.
Metamorphosis can be absent or minimal.

Order 1. Protura

Insects with soft bodies that are minute in size.
No antennae or compound eyes.
There is no metamorphosis.
Mouthparts are bite-sized.
11segments abdomen, plus the telson.
No trachea.
Example: Acerentomon.

Order 2. Thysanura

Tiny primitive bugs.
The body is covered in tiny silvery scales.
Mouthparts that bite with long antennae that are well-developed.
11-segmented abdomen, Cerci and the long telson.
Primitive metamorphosis.
Example: Lepisma (Sliver fish).

Order 3. Aptera

Small, white or light blind insects.
Flattened body.
Chewing with the mouth.
Antennas with many segments.
No caudal filaments.
There is no metamorphosis.
Example: Campodea.

Order 4. Collembola

Insects that are minute; body naked or covered with scales or hair.
Eyes, trachea, Malpighian tubules and metamorphosis.
Mundiatric parts chewing and sucking.
4 – to 6-segmented antennae.
Six-segmented abdomens, typically having a ventral tube Tenaculum, and spring.
Examples: Springtails, Snow flies.

Subclass 2. Pterygota (Metabola) (Gr. Ptera=wings)

Wings are present. They are also lost in some.
No abdominal appendages except cerci.
Metamorphosis that is simple or complicated.

Division1. Exopterygota (Heterometabola)

Wings are developed externally in buds.
Metamorphosis that is simple or primitive.
Young stages are called nymphs.

Order 5. Orthoptera

Large or medium-sized insects.

Two sets of wings. The forewings, or tegmina, are straight and smooth. Hindwings membranous , and folded when they are at rest.
Mouthparts that chew and bite hard.
Large prothorax. Hindlegs jumping.
Compound eyes are usually 3 or more Ocelli.
Short, long, simple, or segmented cerci.
Metamorphosis is simple.
Examples: Locusts, Grasshoppers, Crickets, etc.

Order 6. Grylloblattodea

Small thysanuriform bugs.
There are no wings.
Mouthparts with bites.
Filiform, can have segmented antennae.
Eyes small and compound, no ocelli.
Metamorphosis is simple.
Example: Grylloblatta.

Order 7. Blattaria

Large to medium-sized insects.
The wings are present, or not.
Long, multi-segmented as well as filiform.
Mouthparts chewing and biting types.
The prominent as well as segmented.
Simple metamorphosis.
Examples: Periplaneta, Blatta.

Order 8. Phasmida

Large leaf-like or stick-like insects.
Usually, they are long, filiform and with many segments.
Small compound eyes, ocelli 2, or 3 or not present.
Mouthparts with bites.
The wings are present, or not.
The cerci are small and divided.
Examples: Phyllium, Carausius (Stick insect).

Order 9. Mantodea

Medium-sized to large-sized insects.
A tiny, triangular head has big compound eyes that have three or more Ocelli.
Mouthparts with bites.
A very elongated and elongated prothorax.
Forelegs are modified to catch and holding prey.
Small, big or even without wings.
Metamorphosis is simple.
Examples: Mantis (praying mantis).

Order 10. Dermaptera

Small – to medium-sized insects.
An elongate body with a smooth or chitinous cover.
Mouthparts that bite type.
The abdomen is equipped with a forceps-like cerci located at the rear end.
Metamorphosis is simple.
Example: Forficula.

Order 11. Diploglossata

Small insects.
Depressed body covered in short hairs.
Mouthparts with bites.
There are no eyes or wings.
Two cerci that are segmented is present.
Metamorphosis that is simple.
Example: Hemimerus.

Order 12. Plecoptera

Medium – to large-sized.
Soft-bodied, elongated and flattened insects.
Broadhead has two filiforms of 50 to 100 segmentsed antennas.
Moderate compound eyes , with three or more or none Ocelli.
Mouthparts with bites.
Two pairs of similar veined wings. The hind pair with an enormous anal area.
11 segmented abdomen. The final segment is shortened and bears long, filiform multisegmented cerci.
Hemimetabolous or simple metamorphosis.
The aquatic larva is referred to as Naiads.
Some examples: Stoneflies, Salmon flies.

Order 13. Isoptera

The insects are polymorphic and social in colonies within the caste system.
Small to medium-sized, mostly soft-bodied and light-colored insects.
Small to very big head and has moniliform short or long , many segmented antennae.
Mouthparts chewing or biting.
Eyes with a dingy compound that has 2 or none of the or no.
Wings in two sets when there are two pairs, with similar shape, size and the venation.
Simple and short cerci or 2-8 segments.
Simple metamorphosis.
A colony is made up of males and females who are winged and sterile workers who are wingless soldiers.
Examples include: termites, white ants.

Order 14. Zoraptera

Minute wing or wingless insect.
Antennas with nine segments.
Compound eyes and ocelli can be found in winged forms but are not present in forms with no wings.
Mouthparts that bite type.
The cerci are short and divided.
Simple metamorphosis.
Example: Zorotypus.

Order 15. Embioptera

Small, slender insects that have flattened bodies.

The head’s large size bears an antenna with a filiform shape.
Females with small compound eyes typically larger than males. No Ocelli.
Mouthparts that bite chewing.
Thorax almost length of the abdomen.
The first tarsal segment of the forelegs that has been enlarged to include spinnerets, glands, and glands.
Two pairs of wings at present, membranous and similar in size and size and.
Metamorphosis that is simple or with hemimetabolous.
Example: Oligotoma.

Order 16. Corrodentia

Small insect with wings or winged wings.
The head is large and free. It has long or short filiform antennae.
Usually, large compound eyes are not accompanied by the ocelli.
Mouthparts modified for biting.
No cerci.
Simple metamorphosis.
Some examples: Booklice, Bark lice, Dust lice.

Order 17. Mallophaga

Small ectoparasitic insects with no wings.
Elongated or broad Dorsally flattened, tough and well-chitinised body.
Hypognathic head with no the setiform and clavate antennae.
Eyes reduced to compound eyes, no Ocelli.
Mouthparts with bites.
Short legs with sturdy claws that are designed for securing feathers and hair.
No cerci.
Example of a bird lice.

Order 18. Anoplura

Small-sized to minute-sized, permanent an ectoparasitic species on mammals.
A flattened and long body with no wings.
Small with short , 3-5 segmented setiform antennae on its head.
Reduced eyes or no compound eyes or Ocelli.
Mouthparts that pierce and sucking.
Short legs with one claw specially designed for gripping hairs.
No cerci.
Example: Pediculus (Human louse).

Order 19. Ephemerida

Small to medium-sized, soft-bodied insect with a slender body.
Short setiform antennae.
The mouthparts of the mouth are a bit rusty.
Compound eyes that are wee-developed, and 3 ocelli are present.
One or two pairs of delicate numerous veined wings.
Very long multisegmented, filiform, and multisegmented cerci with the same medial caudal filament.
Metamorphosis that is simple or with hemimetabolous.
Naiad (nymphs) are aquatic creatures with stomach tracheal Gills.
Example: Ephemera (mayfly).

Order 20. Odonata

Medium-sized to large-sized fast-flying predaceous insects.
The head of the mobile bears huge compound eyes as well as Ocelli.
Mouthparts that bite type.
Two pairs of similar thin net-veined wings.
Naiads(nymphs) include aquatic species creatures with or without external gills.
Hemimetabolous or simple metamorphosis.
Examples: Dragonflies, Damselflies.

Order 21. Thysanoptera

Minute, slender, terrestrial insects.
A little dorsally compressed, or nearly cylindrical body.
Short, 6 or 9 segments antennae.
Compound eyes, with 3 ocells present.
Mouthparts that are modified to allow piercing, sucking, and chafing.
Two pairs of wings are both narrow and long with only a only a few veins when they are they are present.
10-11 segmented abdomen , with an ovipositor.
Simple metamorphosis.
Example: Thrips.

Order 22. Hemiptera

Small to large oval or elongated and dorsoventrally flattened terrestrial aquatic insects.
2 to 10 or more rarely 25 , segmented, antennas.
Large eyes, with or without Ocelli.
Mouthparts that are piercing and sucking.
Two pairs of wings when present, fore pair typically thickened at the base and membranous on the apical side in Heteroptera and completely membranous for Homoptera.
No cerci.
Anal respiratory filaments are found in certain aquatic forms as well as male coccids contain anal filaments.
Simple metamorphosis.
The majority of them are phytophagous. Some are predaceous.
Examples: Belostoma, Aphids, Cicadas, scale insects.

Division 2. Endopterygota (Holometabolan)

Metamorphosis complex i.e. completes with pupal and larval stages.
The young stages are also known as larvae.
The wings develop inside pupal cases.

Order 23. Megaloptera

Large- or medium-sized insects.
The prognathous head has numerous slender antennae segmented.
Mouthparts with bites.
Two pairs of wings identical in shape, size and size, and.
No cerci.
Complex metamorphosis involving aquatic larvae.
Examples: Sialis, Corydalus.

Order 24. Neuroptera

Small to medium-sized insect species, mostly terrestrial.
Head hypognathous, has huge and well-separated eye sockets.
Large wings, membranous, many- veined.
Long antennae, usually are filiform.
Mouthparts chewing types.
No cerci.
Larvae can be carnivores. Abdominal gills are present in aquatic larvae.
Complex metamorphosis.
Examples: Crysopa (Lacewing), Myrmeleon (Antlion).

Order 25. Raphidiodea

Elongated, small to moderate-sized delicate terrestrial insects.
Setiform, multiple segmented antennae.
Compound eyes appear prominent with three or more Ocelli.
Mouthparts with bites.
Two pairs of wings that are similar.
Female sporting a and slender Ovipositor.
Complex metamorphosis.
Example: Snake flies serpent Flies.

Order 26. Mecoptera

Slender, small to medium-sized predaceous insects.
Usually elongated and with a vertical head.
Long, filiform and numerous antennas with segments.
Similar, long, membranous wings with narrow wings.
Large and well-separated eye compound, Ocelli 3,, or none.
Mouthparts that bite that have a longer beak.
Short, simple, or 2 segmented cerci.
For males, the top of the abdomen is curved and stings like.
Complex metamorphosis.
Examples: Panorpa (Scorpion Flies).

Order 27. Trichoptera

Small to medium-sized, diurnal and nighttime moth-like insects.
Long, filiform and numerous segmented antennae.
A well-developed compound eye with three or none of the or none.
2 wings that are long hairy, folded roof-like over abdomens.
Mouth part bite the mouth.
One or more segmented cerci.
Complex or the holometabolic metamorphosis.
Larvae aquatic.
Examples: Philopotamus (caddis fly).

Order 28. Lepidoptera

Large to medium-sized flying insects from the terrestrial.
The wings and body are covered with flat, overlapping hairs, and scales.
Antennae vary in their frequency, and can be clavate, serrate either hooked or knobbed, or plumose.
Mouthparts sucking are coiled beneath the head.
Large compound eyes, with 2 or not having Ocelli.
Two pairs of wings, the front pair is usually the largest.
Complex metamorphosis.
Larvae is a caterpillar that has three pairs of thoracic leg and 2 to 4 pairs abdominal prolegs, as well as a chewing mouth.
Examples: Butterflies, Moths.

Order 29. Coleoptera

Large and small insects, with the slender integument.
Antennae vary in size and shape typically 11 segments.
Forewings are leathery (elytra). The hindwings are membranous and fold.
Eyes conspicuous but ocelli absent.
Biting the mouth and chewing the same way.
Usually, abdominals have 10 segments.
No cerci.
Complex metamorphosis.
Examples: Beetles, Weevils.

Order 30. Strepsiptera

Minute to endoparasitic and free-living dimorphic insects.
Short flabellate antennae.
Eyes conspicuous but ocelli absent.
Mouthparts that are atrophied bite-type.
Small white fore-wings, big hind-wings that are fan-shaped.
Metamorphosis complex and hypermetamorphosis.
Example: Stylops.

Order 31. Hymenoptera

Small to huge-sized insects, parasites, or social insects.
Male antennas with 12 segments and 13 in female.
Ocelli is usually present.
Two pairs of wings that are membranous, identical. Each side connected during flight.
Mouthparts that are designed for biting and sucking, lapping, and chewing. The female ovipositor usually produces an abrasive stain.
Abdomen is always covered with a the pedicel that is located at the base.
Complex metamorphosis.
Examples: Wasps, Bee, Ants.

Order 32. Diptera

Medium-sized to minute-sized diurnal, nocturnaland aquatic and terrestrial insects.
Slim body with delicate edges.
Antennae variable, either simple or with the addition of.
Large eyes and separate eyes, with three Ocelli.
Wings 1 pair. Fore-wings designed for flight, and hind-wings used as knob-like halters.
Mouthparts piercing-sucking or sponging.
Complex metamorphosis.
Larvae that are limbless and vermiform, also commonly referred to as maggots.
Examples: Houseflies, Mosquitoes, Midges.

Order 33. Siphonoptera

Small to minute-sized insects that are ectoparasitic to mammals and birds.
A laterally compressed body. In the second instance, wingless.
Small head, with or without eyes and Ocelli.
Capitate and short antennae.
Lengthy and leaping legs.
Mouthparts that are piercing and sucking.
No cerci.
Complex metamorphosis.
Examples: Pulex and Xenopsylla (Fleas).