Phylum Arthropoda- Definition, Classification, Characteristics, Examples

Definition

Phylum Arthropoda comprises animals with the bilateral, triploblastic, segmented and coelomate organization.

They have an exoskeleton made up of Chitin and jointed appendages used for locomotion, feeding and other purposes. They are known from Palaeozoic era. Some 9,50,000 species or more are known. They are intimately related to man and hence are important.

Brief History

  • Arthropods were known to man from the very early historical period.
  • Aristotle (322 B.C.) described a few insects and crabs.
  • Charak (1st century A.D.) described few useful and harmful arthropods in his book, Charak Samhita.
  • Linnaeus created a group Insecta and placed all the arthropods in it.
  • Lamark reorganised this group and subdivided it into classes, i.e., Crustacea, Hexapoda and Arachnida.
  • Von Siebold (1845) created the phylum Arthropods.

General Characteristics of Arthropoda

  • The representatives of Phylum-Arthropoda are characterized by the presence of jointed appendages with varied functions (Gr. Arthos = jointed, pods = foot).
  • They are bilaterally symmetrical, triploblastic metazoans with a segmented body.
  • The Organ-system level of body organization is found in Arthropoda.
  • The body is covered with a thick, hard exoskeleton which is made up of chitin. The exoskeleton is periodically shed through moulting.
  • The body is divisible into three parts, head, thorax and abdomen. The Head and thorax are generally fused to form a cephalothorax.
  • The coelom is haemocoel.
  • The digestive system is well developed, mouthparts are adapted to different modes of feeding.
  • Gills, trachea, book-lungs are the organs of respiration.
  • The ventral nerve cord is double and a brain is present anteriorly.
  • Ocellia and compound eyes are present.
  • The malpighian tubule and the green glands are excretory organs.
  • Sexes are separate.
  • Gonads and gonoducts are well-developed.
  • Many larval stages are present in the life cycle, but it may be direct as well.
  • Nearly 9,50,000 species are known which thrive all kinds of habitats.
  • Examples of Arthropoda are:

Classification of Arthropoda

Classification of Arthropoda
Classification of Arthropoda

Class 1: Crustacea

  1. Head and thorax fused to form cephalothorax.
  2. Body with dorsal carapace. Exoskeleton is flexible, impregnated with CaCO3 salts.
  3. Appendages often biramous.
  4. Respiration by gills.
  5. Head consist of 5 segments with pairs of antennae, a pair of mandibles, 2 pairs of maxillae and a pair of staked compound eyes.
  6. Sexes are separate.

Subclass 1: Branchiopoda

ORDER:

  1. Anostraca- Ex: Artemia
  2. Notostraca Ex: Apus
  3. Cladocera Ex: Daphnia
  4. Chonchostraca Ex: Lynceus

Subclass 2: Ostracoda

ORDER

  1. Mydocopa Ex: Cypridina
  2. Podocopa Ex: Cypris
  3. Platycopa Ex: Cytherella

Subclass 3: Copepoda

Example: Cyclops

Subclass 4: Mystacocarida

Example: Derecheitocarus

Subclass 5: Branchiura

Example: Argulus

Subclass 6: Cirripedia

ORDER:

  1. Troracica Ex: Balanus, Lepas
  2. Acrothoracia Ex: Alcippe
  3. Ascothoracia Ex: Synagoga
  4. Apoda Ex: Proteolepas

Subclass 7: Malacostraca

ORDER:

  1. Nebaliacea Ex: Nebalia
  2. Anaspidacea Ex: Anaspides
  3. Bathynella Ex: Bothynella
  4. Somatopoda Ex: Squilla
  5. Mysidacea Ex: Mysis
  6. Cumacea Ex: Diasyslis
  7. Tanaidacea Ex: Apseudes
  8. Isopoda Ex: Oniscus
  9. Amphipoda Ex: Caprella
  10. Decapoda Ex: Palaemon

Class 2: Myriapoda

  1. Gr. Myrios = ten thousand; Podos = foot.
  2. Body elongated and cylindrical.
  3. Body divisible into head and trunk.
  4. One pair of antennae, one pair of mandibles present.
  5. One or two pairs of legs are present in each segment.
  6. Respiration by means of trachea.
  7. Centipedes and Millipedes.

ORDER:

  1. Diplopoda Ex: Julus (Millipede)
  2. Chilopoda Ex: Scolopendra (Centipede)

Class 3: Insecta

  1. Body is divided into head, thorax and abdomen.
  2. Head consists of 6 segments, thorax consists of three segment and abdomen of 11 segments.
  3. Head bears a pair of compound eyes, a pair of antennae, a pair of mandibles and two pair of maxillae.
  4. Thorax bears 3 pairs of legs and 2 pairs of wings.
  5. Abdomen devoid of appendages.
  6. Tracheae open to outside by spiracles.
  7. Sexes separate, fertilization internal.

Subclass 1: Apterygota

ORDER:

  1. Protura Ex: Acerentulus
  2. Collembola Ex: Achorutes
  3. Thysanura Ex: Lepisma
  4. Deplurab Ex: Japyx

Subclass 2. Pterygota

Order

  1. Orthoptera Ex. Mantis.
  2. Isoptera Ex. Termites
  3. Neuroptera Ex. Lacewings
  4. Ephemerida Ex. Mayflies
  5. Odonata Ex. Dragonflies
  6. Plecoptera Ex. Stoneflies
  7. Corrodentia Ex. Booklice
  8. Mallophaga Ex. Lice
  9. Thysanoptera Ex. Thrips
  10. Anoplura Ex. Pediculus
  11. Hemiptera Ex. Cimex
  12. Homoptera Ex. Cicada
  13. Dermaptera Ex. Forficuta
  14. Coleoptera Ex. Beetles
  15. Mecoptera Ex. Scorpion flies
  16. Trichoptera Ex: Caddisflies
  17. Lepidoptera Ex. Butterflies
  18. Diptera Ex. Musca, Anopheles
  19. Siphonaptera Ex. Fleas

Class 4. Arachnida

  1. Gr. Arachne = spider.
  2. Terrestrial or aquatic forms.
  3. Body divided into cephalothorax or prosoma and abdomen or opisthosoma.
  4. Cephalothorax with 2 chelicerae, 3 pedipalpi 4 pairs of walking legs and simple eyes.
  5. Opisthosoma without legs.
  6. Jaws and antennae absent.
  7. Respiration by tracheae, book gills and book lungs.
  8. Excretion by coxal gland and Malpighian tubules.
  9. Dioecious, mostly oviparous.
  10. Courtship dance before mating.

ORDER:

  1. Scorpionida Ex: Scorpion
  2. Pseudoscorpionidae Ex: Chelifer
  3. Sohfugae Ex: Galeodes
  4. Palpigardi Ex: Koenenia
  5. Uropygi Ex: Mastigoproutus
  6. Amblypygi Ex: Charinus
  7. Araneida Ex: Argiope
  8. Picinulei Ex: Ricinoides
  9. Opiliones Ex: Phalaglim
  10. Acarina Ex: Sarcoptes

Class 5. Onychophora

  1. Found in crevices of stones in moist places.
  2. The body is elongated and worm-like.
  3. Due to the presence of legs, the body appears to be divided into segments.
  4. The genital aperture is situated in front of the anus.
  5. The legs are muscular, stumpy and provided with claws.
  6. Respiration by tracheae,
  7. Excretory organs are a pair of nephridia.
  8. Sexes are separate.
  9. Ex. Peripatus

Some Examples of Arthropoda

These are some of the common examples of Arthropoda:

  1. Palaemon Malcolmsoni (Prawn)
  2. Eupagurus (Hermit Crab)
  3. Scolopendra (Centipede)
  4. Julus (Millipede)
  5. Periplaneta americana (Cockroach)
  6. Schistocerca (Locust)
  7. Musca (Housefly)
  8. Danus (Butterfly)
  9. Leptocoriza (Rice Bug)
  10. Limulus (King Crab)
  11. Argiope
  12. Palamnaeus (Scorpion)
  13. Peripatus

Let us know about them in more detail, one-by-one.

PALAEMON MALCOLMSONI (PRAWN)

Classification of Palaemon Malcolmsoni

Phylum Arthropoda
ClassCrustacea
OrderDecapoda
GenusPalaemon
Speciesmalcolmsoni

Distribution: It is commonly found in India.

Habits and Habitats:

  1. It is found in fresh water ponds, lakes, ditches, streams etc. on muddy bottom.
  2. It is nocturnal, i.e., becomes active at night, and is carnivorous.

Characteristics Features of Palaemon malcolmsoni

  1. It is commonly known as Prawn.
  2. The body is elongated, spindle-shaped, growing up to 25 cms in length and has a deep orange-coloured body wall.
  3. The body is divided into cephalothorax and abdomen.
  4. There are 19 segments in the body:-
    1. Cephalic 5 segments
    2. Thoracic 8 segments
    3. Abdominal 6 appendages.
  5. The cephalothorax is anteriorly produced into a rostrum with spines.
  6. 19 pairs of appendages are present on the body-
    1. Cephalic appendages: Antennule, antenna, mandible, maxilula and maxilla.
    2. Thoracic appendages: I, II, III maxillipedes and five pairs of walking legs.
    3. Abdominal appendages: 5 pairs of pleopods and one pair of the uropod.
  7. Sexes are separate, sexual dimorphism is present, fertilization is external and development is direct without a larval stage.
  8. It is cultured and is exported to earn foreign exchange.
  9. It provides palatable food.
Palaemon malcolmsonii (Prawn) – Labeled Diagram

EUPAGURUS (Hermit Crab)

Classification of Eupagurus

Phylum Arthropoda
ClassCrustacea
OrderDecapoda
GenusEupagurus

Distribution: Cosmopolitan in distribution, found from Alaska to Lower Carlifronia and Main to Florida.

Habits and Habitats:

Eupagurus is found inhabiting the empty shells of marine gastropods usually with appendages protruding out.

Characteristics Features of Palaemon malcolmsoni

  1. Commonly known as Hermit crab.
  2. The body is divided into cephalothorax and abdomen.
  3. The first pair of thoracic legs are chelate and protrude out of the gastropod shell, while the last two pairs are reduced.
  4. The abdomen is curved with hook-like uropods.
  5. The body is modified to adjust the coils of gastropods shell as under:
    1. Right chelate is large as compared with left.
    2. The abdomen is asymmetrical, soft and coiled.
    3. Abdominal appendages of the right side are absent and those of the left side are reduced.
    4. Uropods are hooked and notched to hold the shell.
  6. Five pair of walking thoracic legs are present.
  7. The first pair of thoracic legs are chelate, forming the large pinching claws.
  8. The abdomen is reduced and fixed under the cephalothorax. It is permanently bent under the cephalothorax fitting into a groove in the thoracic sterna, thus remaining invisible in dorsal view.
  9. Development in indirect, zoea and megalopa larval stages are present.
  10. It is also also used as food.
Eupagurus (A) Entire animal. (B) Showing commensalism with sea anemone

SCOLOPENDRA (Centipede)

Classification of Scolopendra

Phylum Arthropoda
ClassMyriapoda
SubclassOpisthogoneata
OrderChilopoda
GenusScolopendra

Distribution: Scolopendra is found in India and America.

Habits and Habitats:

  1. Scolopendra is terrestrial, found under stones, barks and decaying wood.
  2. Carnivorous and nocturnal. It becomes active at night and feeds upon insects and worms.

Characteristics Features of Scolopendra

  1. It is commonly known as Centipede or Hundred Legger.
  2. The body is elongated, dark greenish-brown in color and dorsoventrally flattened.
  3. The body is divisible into head and trunk.
  4. The head contains paired antennae, ocelli, mandibles and maxillae.
  5. Body consists of 21 segments and a pair of legs is present in each segment.
  6. First pair of legs modified to form poison claws.
  7. Tracheae is open to the outside by spiracles.
  8. Anus is present on the last segment below genital atrium.
  9. Harmful to man as its poison causes pain, dizziness, headache and fever.
Scolopendra Labelled Diagram

JULUS (Millipede)

Classification of Julus

Phylum Arthropoda
ClassMyriapoda
SubclassProgoneata
OrderDiplopoda
GenusJulus

Distribution: It has cosmopolitan distribution, found in India, Europe and USA.

Habits and Habitats:

  1. Julus or millipede is a terrestrial arthropod, usually found in damp and dark places.
  2. It feeds on decaying organic material and is a slow-moving animal.
  3. When distributed, usually rolls up into a tight spiral and emits a disagreeable odour from the segmental scent gland.

Characteristics Features of Julus

  1. Popularly known as Millipede or Thousand Lagger, due to the presence of numerous legs.
  2. Body is elongated and more or less cylindrical.
  3. Body is divisible into head and trunk.
  4. Head is covered by a shield and consists of 7 pairs of jointed antennae, ocelli, and mandibles.
  5. The anterior region of trunk, consisting of four segments with legs is termed as thorax.
  6. Two pair of walking legs are present on each trunk segment, except the first four and last abdominal segment.
  7. The trunk consist of 40 segments.
  8. Odoriferous glands open on terga.
  9. It is a slow moving animal.
Julus Labeled Diagram

PERIPLANETA AMERICANA (Cockroach)

Classification of Periplaneta Americana

Phylum Arthropoda
ClassInsecta
SubclassPterygota
DivisionExopterygota
OrderOrthoptera
GenusPeriplanata
Speciesamericana

Distribution: It is found in India, Asia and USA. It has original home in Mexico but has travelled with man to all parts of the world. They flourish chiefly in tropical, damp forests but occurs throughout the world.

Habits and Habitats:

  1. Periplaneta is found in warm and damp places like the kitchen, hotel, restaurants, godowns, stores, ships etc.
  2. It is nocturnal, i.e., active during the night, cursorial and omnivorous.

Characteristics Features of Periplaneta Americana

  1. Commonly known as Cockroach.
  2. The body is dorsoventrally flattened.
  3. The body is divisible into a head, thorax and abdomen.
  4. The Head is small, containing eyes and mouthparts.
  5. The mouthparts are biting and chewing type and have labrum, mandibles, maxillae, labium and hypopharynx.
  6. The thorax is divisible into (i) prothorax (ii) mesothorax (iii) metathorax
  7. The thorax has three pairs of walking legs and two pairs of wings.
  8. The abdomen has ten segments.
  9. The male has anal styles and cerci.
  10. Sexes are separate, development includes incomplete metamorphosis.
Periplaneta americana (A) Dorsal View (B) Ventral View

SCHISTOCERCA (Locust)

Classification of Schistocerca

Phylum Arthropoda
ClassInsecta
SubclassPterygota
DivisionExopterygota
OrderOrthoptera
GenusSchistocerca

Distribution: Commonly found in Africa, Arabia, India, Japan, Maxico, Philippines and Afghanistan.

Habits and Habitats:

  1. Most widely distributed locust, essentially found in dry deserts.
  2. It is herbivorous, gregarious and migratory, can fly over long distances.
  3. It is the worst destroyer of green vegetation like crops and orchards.

Characteristics Features of Schistocerca

  1. Commonly known as Locust.
  2. Body is divided into head, thorax and abdomen.
  3. The head lies into prothorax with mouth downwards (Hypognathous head).
  4. Chewing and biting type of mouth parts.
  5. Three pairs of walking legs for jumping and crawling.
  6. Forewings are leathery and hindwings are membranous.
  7. Abdomen consists of eleven segments.
  8. Sexes are separate, male has anal styles and female has indistinct ovipositor.
  9. Generally found in migratory and non-migratory phases.
  10. During migratory phase, locusts invade the fields and cause much damage to crops.
Schistocerca (Locust) Labeled Diagram

MUSCA (Housefly)

Classification of Musca

Phylum Arthropoda
ClassInsecta
SubclassPterygota
DivisionExopterygota
OrderDiptera
GenusMusca

Distribution: Cosmopolitan in distribution.

Habits and Habitats:

Housefly is present around us. Specially it sits upon dead organic debris, kitchen, hotels, diaries and horse manure.

Characteristics Features of Musca

  1. Housefly is universally present throughout the world.
  2. Inhabits kitchen, hotels, dairies, horse manure and dead organic debris.
  3. The body is fairly well built, there are four dark lines on the thorax.
  4. Head with a pair of compound eyes, three ocelli and a pair of small antennae.
  5. Sponging type of mouthparts presents to suck the liquid food or semisolid food.
  6. There is one pair of wings only, the second pair of wings is changed into halters.
  7. It has to regurgitate habit and contaminates the food and drinks by dropping the germs and bacteria in it.
  8. Spread diseases such as cholera, tuberculosis, typhoid, dysentery etc.
  9. Development indirect, larval and pupal stages are present.
Musca (Housefly) – Labeled Diagram

DANUS (Butterfly)

Classification of Danus

Phylum Arthropoda
ClassInsecta
SubclassPterygota
DivisionExopterygota
OrderLepidoptera
GenusDanus

Distribution: Cosmopolitan in distribution.

Habits and Habitats:

It is one of the common butterflies of India. It feeds on plant juices and the nectar of flowers. It is a diurnal inhabit.

Characteristics Features of Danus

  1. The body is covered with scales with many attractive and colourful patterns.
  2. The body is slender, the head containing a pair of club-shaped antennae and compound eyes.
  3. There are two pairs of membranous wings. Venation is clearly seen on wings.
  4. Wings are kept folded during the resting stage.
  5. The mouthparts are of siphoning type.
  6. Maxillar elongated, tubular and form a spring-like coiled proboscis, mandibles are absent.
  7. They are diurnal, ie, remain active in the daytime.
  8. Unisexual, fertilization is external.
  9. Development is indirect, metamorphosis is complete and the larva is known as a caterpillar.
Danus (Butterfly) – Labeled Diagram

LEPTOCORIZA (Rice-bug)

Classification of Leptocoriza

Phylum Arthropoda
ClassInsecta
SubclassPterygota
DivisionExopterygota
GenusLeptocoriza

Characteristics Features of Leptocoriza

  1. It is commonly known as Rice-bug or Rice Gandhi.
  2. It has two pairs of wings.
  3. Mouth parts are adapted for piercing the plant tissue.
  4. It feeds mainly on the sap developing grains of paddy and also the seeds.
  5. Mandibles and maxillae are style-like in the grooved labium.
  6. Metamorphosis is incomplete.
  7. It is a serious pest of paddy.
Life history of Leptocoriza (Rice Bug)- A. Eggs B. Nymph C. Adult

LIMULUS (King Crab)

Classification of Limulus

Phylum Arthropoda
ClassArachnida
OrderXiphosura
GenusLimulus

Distribution: Found in eastern coast of Asia and its Islands and eastern coast of North America from Nova Scotia to Florida.

Habits and Habitats:

They live for the most part in seawater a few fathoms deep, where plough mud.

Characteristics Features of Limulus

  1. It is commonly known as King Crab.
  2. It has a majestic look.
  3. Body is divisible into a broad horseshoe-shaped prosoma and triangular opisthosoma.
  4. Prosoma is convex, shield-like with one pair of median and two pair of lateral eyes.
  5. Prosoma contains one pair of short chelicerae, one pair of pedipalpi and 4 pairs of walking legs.
  6. The opisthosoma is composed of 9 segments. It contains 6 pairs of spines, genitals operculum and book gills. Book gills are used for “Respiration”.
  7. The post and caudal spine is movable.
  8. They are the oldest member of Arachnida and have a long fossil history.
  9. As it is an extremely primitive marine Arthropod, it is called living fossil.
Limulus (A) Dorsal View (B) Ventral View

ARGIOPE

Classification of Argiope

PhylumArthropoda
ClassArachnida
OrderAraneida
GenusArgiope

Characteristics Features of Argiope

  1. It is generally found in houses and gardens.
  2. It is carnivorous and feed upon insects.
  3. The body is divisible into an anterior prosoma and a posterior opisthosoma.
  4. Prosoma and opisthosoma are joined by a narrow pedicel.
  5. Prosoma is covered by a carapace having eight ocelli.
  6. The prosoma has sub chelate chelicerae with poison glands and six joined pedipalpi.
  7. Opisthosoma is unsegmented, soft, rounded and without telson.
  8. Spinnerets presents in the opisthosoma which produce silk threads for the construction of spider web.
  9. Book lungs are the organs of respiration.
  10. Sexes are separate and sexual dimorphism is well pronounced.
Argiope (A) Dorsal View (B) Ventral View

PALAMNAEUS

Classification of Palamnaeus

PhylumArthropoda
ClassArachnida
OrderScorpionida
Genuspalamnaeus

Distribution: Cosmopolitan, specially found in tropical and subtropical countries like India, USA and Europe.

Habits and Habitats:

  • It is found in damp places under stones, fallen leaves, bark of trees etc.
  • It is nocturnal and carnivorous.

Characteristics Features of Palamnaeus

  1. It is commonly known as Scorpion.
  2. The body is elongated and segmented. Body color is dark brown or black.
  3. The body is divided into (i) Prosoma-anterior part, and (ii) Opisthosoma-posterior part.
  4. Opisthosoma is subdivided into-
    1. Mesosoma-composed of 7 segments and
    2. Metasoma composed of 5 segments.
  5. Prosoma is covered by dorsal carapace and six appendages, namely-chelicerae, pedipalpi and four pairs of walking legs.
  6. The body is oval, the dorsal surface is flat and segmented.
  7. Capitulum: is protruding and contains chelicerae and pedipalpi.
  8. Scutum is shield-shaped and completely covers the body in male.
  9. Four pairs of walking legs are present, with the adhesive disc.
  10. It is a carrier of several disease-causing germs and bacteria.
  11. The dorsal body wall is the tergum, the ventral body wall in the sternum, both are joined by the pleuron.
  12. Genital operculum and pectines are present on the ventral side of the mesosoma.
  13. Metasoma is limbless.
  14. The last segment of metasoma bears a sting mode up of the ampulla and spine.
  15. The poison causes pain, fever and even death to man.
Palamnaeus Labeled Diagram

PERIPATUS

Classification of Peripatus

PhylumArthropoda
ClassOnychophora
GenusPeripatus

Distribution: Peripatus has discontinuous distribution. It is found in damp forests of Malaysia, Africa, South Africa, Australia and New Zeeland.

Habits and Habitats:

  • Peripatus are terrestrial, nocturnal, predaceous, carnivorous and shy creature and lives under bark, logs, stone, the crevice of rocks and other permanently damp, dark and warm places.

Characteristics Features of Peripatus

  1. They are found in crevices of stones in moist places.
  2. The body is elongated and worm-like.
  3. Due to the presence of legs, the body appears to be divided into segments.
  4. The genital aperture is situated in front of anus.
  5. The legs are muscular, stumpy and provided with claws.
  6. Respiration takes place by tracheae.
  7. Excretory organs are a pair of nephridia.
  8. Sexes are separate.
Peripatus Labeled Diagram

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