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:
- 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.
- 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.
- 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.
- 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:
- 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
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