Phylum-Arthropoda

Phylum-Arthropoda – (The name is derived from- Atheros-joint, pods-appendages). These are invertebrates include insects, arachnids, myriapods, and crustaceans. Phylum Arthropoda is the largest phylum of the kingdom Animalia. Around two-thirds of all species on earth belongs to the phylum Arthropoda.

Characteristics features of phylum Arthropoda

• Level of organization: The members having the organ-system level of organization.
• Symmetry: Bilateral symmetry in organisms
• Germinal layer: Triploblastic
• Segmented body
• Body cavity or coelom: These are coelomate animals.
• Exoskeleton: In arthropods, the body is covered with a chitinous exoskeleton.
• Body: The body of the members divided into head, thorax, and abdomen. They consisting of Joint appendages (jointed legs).
• Respiration: Through gills, book gills, book lungs, or tracheal system.
• Circulation: Open type of circulatory system consisting of hemolymph.
• Sensory organs are found like antennae, eyes- may be compound and simple. Balancing organs or statocytes is present.
• Excretion: Malpighian tubules as an excretory organ.
• Reproduction: The members of this phylum are mostly dioecious.
  • Generally Internal Fertilization
  • Mostly oviparous- (these lay eggs.)
• Development-It may be Direct or Indirect development is seen in members.

Scientific Classification of Arthropoda

The Arthropods divided into four major classes:

Crustacea

•  Members including animals like crabs, lobsters, crayfish, shrimps, prawns, etc.
• mostly these are free-living aquatic animals, some terrestrial and some parasitic, few are sessile also.
• Crustaceans possess an exoskeleton,  by which they moult to grow.
• Distinguished from other groups of arthropods by possessing biramous i.e. limbs in two parts.
• Larval forms as nauplius stage of branchiopods and copepods.

Myriapoda

•  Members of this group including millipedes, centipedes, and others.
• These consisting mostly of simple eyes, and Single pair of antennae.
• They breathe through the spiracles which is connected to the tracheal system.
• Excrete nitrogenous waste by malpighian tubules.

Insecta

• Direved from Latin word- insectum, 
• These are the largest group of phylum Arthropoda, subphylum-Hexapoda.
• possess a chitinous exoskeleton
• Body divided into three parts: head, thorax, and abdomen
• The members consisting three pairs of jointed legs, compound eye, and one pair of antennae.
• The pupal stage is found in these groups which undergo four-stage metamorphosis.
• Some insects lack pupal stage, undergo three-stage metamorphosis, and develop through the nymphal stage.

Arachnida

• These arthropods belong to the subphylum Chelicerata.
• These are mainly terrestrial
• Most of these consist of eight legs, the front pair of legs in some species working as a sensory organ.
• They have two types of eyes: Lateral and median ocelli.
• The lateral ocelli are evolved from compound eyes.
• The median ocelli- developed from the transverse fold of the ectoderm.
• They don’t possess antennae or wings.

 Some Economically important Arthropoda:

• • Bombyx-Silkworm
  • Apis-Honey bee
  • Laccifer- Lac insect
• Some are vectors of disease: Mosquitoes like Anopheles, Culex, and Aedes.
• Gregarious pest (a harmful pest that attacks crops): Locusta- Locust,
• Living fossil– Limulus-King crab

You can also read:

• Phylum Porifera
• Phylum Coelenterata
• Phylum Ctenophora
• Phylum Platyhelminthes
• Phylum-Annelida