PHYLUM ARTHROPODA

HISTORY

Although invertebrates evolved 500 million years ago, their fossil record is poor due to lack of hard skeleton. Phylum Arthropoda were first to have hard exoskeleton made of chitin, a nitrogenous polysaccharide made of hexoses some of which contained amino or acetyl groups and jointed appendages. Coelom evolved in annelids was replaced by haemocoel. It has been suggested that the need for a hydrostatic skeleton disappeared with the advent of jointed exoskeleton and the coelom no longer required for this purpose was replaced by the cavity of blood stream (haemocoel). Dr. S. M. Manton (Zool. J. linn, Soc. 51 : 203-400, 1972) postulates polyphyletic origin of Phylum Arthropoda Evolutionary and adaptive potentialities of Arthropods have been tremendous.

Phylum Arthropoda include crabs, shrimps, barnacles and other crustaceans in class Crustacea; insects in class Insecta; spiders, scorpions, ticks and their allies in class Arachnida; centipedes in Chilopoda; millipedes in Diplopoda and other less familiar and fossil forms. Arthropods are adapted for life in air, water and land. Some occur at altitude of 20,000 feet on mountains and crustaceans to depths of more than 32,000 feet in the sea.

Phylum Arthropoda are free living, parasitic on plants and man and his animals. Some are gregarious. Phylum Arthropoda are economically very important. Large crustaceans crabs, lobsters, shrimps are eaten by man; small crustaceans are staple foods for fishes. The insects and spiders are eaten by land vertebrates. Insects are friends as well as worst enemy and competitor of man eating his crops, stored food, goods and clothes besides carrying and spreading several diseases like malaria and filaria, etc. Some important products like honey, lac and silk are derived from insects. It is also a fact that insects have been responsible for evolution of Angiosperms.

DIAGNOSTIC CHARACTERS OF PHYLUM ARTHROPODA

Jointed legs (appendages)
Exoskeleton of chitinous cuticle.
Coelom replaced by haemocoel.
Open circulation.
Compound eyes.
Sexes separate.
Largest group.

CLASSIFICATION OF PHYLUM ARTHROPODA

CLASS I CRUSTACEA

Head and thorax fused to form cephalothorax covered with carapace.
Appendages biramous.
Antennae 2 pairs

Sub-class A. Branchiopoda

Small freshwater crustaceans.
Trunk appendages serve as gills.

Order 1 Anostraca

1. Called as fairy shrimps.
2. Carapace absent. Trunk elongated.
  Example :- Branchipus, Artemia, Eubranchipus

Order 2 Notostraca

1. Carapace present.
2. Anterior trunk bears 35 to 70 pairs of appendages.
  Example :- Apus, Lepidurus.

Order 3 Conchostraca

1. Small crustaceans.
2. Carapace present.
  Example :- Lyneus, Estheria.

Order 3 Cladocera

1. 1. 1. Includes clamshrimps and water fleas.
    2. Body laterally compressed.
      Example :- Cyzicus, Daphnia.

Sub-class B. Ostracoda

Seed shrimps.
Body enclosed in a bivalve carapace.
Example :- Cypris, Eucypris.

Sub-class C. Copepoda

Small crustaceans. Body divided into head thorax and abdomen.
5 pairs of thoracic appendages.
Example :- Cyclops, Condracanthus, Calanus.

Sub-class D. Brachiura

Ectoparasites of skin and gills.
4 large and biramous thoracic appendages with swimming setae.
Example :- Argulus, Dalos.

Sub-class E. Cirripedia

Called as Barnacles.
Adults sessile or parasitic.

Order 1 Thoracica

1. Sessile forms.
2. Trunk appendages 6 pairs.
  Example :- Lepus, Balanus

Order 2 Acrothoracica

1. 4 pairs of trunk appendages.
2. Bore into mollusc shell and soft corals.
  Example :- Alcippe, Cryptothialus

Order 3 Ascothoracica

1. 6 pairs of trunk appendages.
2. Parasites on echinoderms and soft corals.
  Example :- Syngoga, Dendrogaster.

Order 4 Apoda

1. Parasitic trunk appendages absent.
2. Body divided into rings.
  Example :- Proteolepas.

Order 5 Rhizocephala

1. Parasitic crustaceans.
2. Appendages absent. Stack sends branches into the host.
  Example :- Sacculina.

Sub-class F. Malacostraca

Carapace covers head and thorax.
Trunk contains 8 thoracic and 6 abdominal segments.

Order 1 Nebaliacea

1. Carapace bivalved.
2. Abdominal segments 7.
  Example :- Nebalia.

Order 2 Mysidacea

1. Carapace thin and covers thorax only.
2. Body elongated. Uropod forms fantail.
  Example :- Mysis

Order 3 Amphipoda

1. Carapace absent. Gills thoracic.
2. Body elongated and laterally compressed.
  Example :- Gammarus, Caprella, Cerapus.

Order 4 Isopoda

1. Body dorsoventrally flattened with short abdomen.
2. Carapace absent.
3. Free living or parasitic.
  Example :- Oniscus, Limnoria, Bopyrus.

Order 5 Stomatopoda

1. Carapace small.
2. Abdomen large and broad.
  Example :- Sauilla, Pseudosquilla.

Order 6 Decapoda

1. Prawns, shrimps, crayfishes, lobsters and crabs.
2. Carapace on cephalothorax.
3. Legs 5 pairs.

Sub-order 1 Macrura

1. Abdomen well developed and hard.
2. 18 pairs of appendages.
  Example :- Penaeus, Palinurus, Palaemon, Lucifer,
  Astacus, Homarus.

Sub-order 2 Anomura

1. Abdomen flexed.
2. Commensal or free living.
  Example :- Eupagurus, Galathea, Hippa.

Sub-order 3 Brachyura

1. Common crab.
2. Abdomen reduced.
  Example :- Cancer, Carcinus, Mala.

CLASS II ARACHNIDA

Body divided into prosoma and opisthosoma.
First pair of appendages are feeding chelicerae.
Antennae absent.

Order 1 Xiphisura

1. Cephalothorax horse shoe shaped.
2. Abdomen unsegmented.
  Example :- Limulus.

Order 2 Scorpionida

1. Body divided into prosoma, mesosoma and metasoma.
2. Respiration by book lungs.
  Example :- Scorpions, Buthus, Palaeminaeus.

Order 3 Araneida

1. Prosoma and opisthosoma joined by a narrow stalk.
  Example :- Spiders, Lycosa, Agelena

Order 4 Palprigradi

1. Chelicerae large.
2. Carapace has 2 plates.
  Example :- Koenema.

Order 5 Pedipalpi

1. Small arachnids.
2. Pedipalps on legs.
  Example :- Tarantula, Phrynichus.

Order 6 Chelonethida

1. Prosoma of 6 fused segments covered with carapace.
2. Opisthosoma with 12 segments without sting.
  Example :- Chelifer, Garypus.

Order 7 Phalangida

1. Prosoma joined to abdomen.
2. Chelicerae small 3 jointed.
  Example :- Phalangium, Leiobonum.

Order 8 Acarina

1. Body oval compact, with no differentiation of prosoma and opisthosoma.
  Example :- Ticks and mites, Sarcoptes, Ixodes, Argas.

Order 9 Solpugida

1. Prosoma divided into large anterior and small posterior part.
2. Chelicerae very large.
  Example :- Galeodes

CLASS III PAUROPODA

Body divided into head and trunk.
Head has a pair of antennae, one pair of mandibles and maxillae forming lower lip.
Example :- Pauropus.

CLASS IV SYMPHYLA

Head with one pair of antennae, one pair of mandibles and two pairs of maxillae.
Example :- Garden centipedes, Scolopendrella, Scutigerella.

CLASS V DIPLOPODA

Body divided into head and trunk.
Each trunk segment bears 2 pairs of legs.
Example :- Millepedes, Julus, Spirobolus.

CLASS VI CHILOPODA

Body divided into head and trunk.
Each trunk segment bears 1 pair of legs.
Example :- Theotops.

CLASS VII ONYCHOPHORA

Primitive arthropods.
Contain annelidan and arthropodan character.
Example :- Peripatus.

CLASS VII ONYCHOPHORA

Body divided into head thorax and abdomen.
Thorax contains 3 pairs of legs and 1 or 2 pairs ofwings

Sub·class A. Apterygota

Wingless insects.
Little or no metamorphosis.

Order 1 Thysanura

1. Long antennae.
2. Chewing mouth parts.
  Example :- Lepisma.

Order 2 Protura

1. Antennae and compound eye absent.
2. Appendages on abdomen.
  Example :- Acerentulus.

Order 3 Collembola

1. Mouth parts chewing or sucking.
2. Furcula (Springing organs on ventral side of 4th abdominal segment).
  Example :- Achorutes

Sub·class B. Pterygota

Wings present.
Metamorphosis prevalent.

Division I Exopterygota
1. Wings develop externally.

Order 4 Orthoptera

1. Two pairs of wings.
2. Chewing mouth parts.
3. Incomplete metamorphosis.
  Example :- Cockroach (Periplaneta), Locust (Schistocerca), Grasshopper (Melanopus), Gryllys, Grylotapla, Leaf insect (Phyllium), Praying mantis.

Order 5 Dermaptera

1. Fore wings small and leathery Hind wings large and membranous.
2. Mouth parts chewing.
  Example :- Earwigs (Foificula)

Order 6 Isoptera

1. Social insects with castes.
2. Wings two parts.
  Example :- Termites or white ants.

Order 7 Placoptera

1. Hind wings usually folded under forewings at rest.
2. Mouth parts chewing.
  Example :- Isoperla (Stonefly).

Order 8 Anoplura

1. Wingless ectoparasites.
2. Claws for clinging to hairs.
3. Piercing and sucking mouth parts.
  Example :- Pediculus

Order 9 Ephemeroptera

1. Membranous wings. Forewings larger than hind wings.
2. Two or three abdominal tails.
  Example :- Ephimera (May fly)

Order 10 Odonata

1. Wings membranous. Hind wings usually larger than forewings.
2. Body tusk like. Antennae short.
  Example :- Dragonflies, Damselflies.

Order 11 Hemiptera

1. Wings two pairs.
2. Mouth parts piercing and sucking forming beak like organ.
  Example :- Cimex (Bed bug), Bellostoma, Ranatra, Nepa, Aphids, Cicada.

Order 9 Solpugida

1. Prosoma divided into large anterior and small posterior part.
2. Chelicerae very large.
  Example :- Galeodes

Division II Endopterygota
1. Wings develop internally.

Order 12 Trichoptera

1. Wings membranous, 2 pairs and covered with long hairs.
2. Mouth parts vestigeal.
  Example :- Caddis flies

Order 13 Hymenoptera

1. Wings same size (2 pairs).
2. Mouth parts chewing-Lapping.
  Example :- Apis (Honey bee), Bees, Wasps, Sawflies, Bumble
  bees.

Order 14 Diptera

1. Wings one pair. Hind wings as halters.
2. Piercing-sucking or sponging mouth parts.
  Example :- Flies (Musca), Mosquitoes (Anopheles, Culex, Aedes), Gnats, Blowflies, Botflies, etc.

Order 15 Lepidoptera

1. Membranous wings covered with overlapping scales.
2. Mouth parts sucking.
  Example :- Butterflies, moths.

Order 16 Coleoptera

1. Forewing hard, hind wing membranous and folding.
2. Body covering hard and chitinous.
  Example :- Beetles.

Order 7 Siphonoptera

1. Ectoparasite wingless.
2. Piercing-sucking mouth parts.
  Example :- Fleas (Xenopsylla).

REFERENCES :-

https://en.wikipedia.org/wiki/Arthropod
https://www.amazon.in/Practical-Zoology-Invertebrate-S-Lal/

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