Phylum Arthropoda – Class 11 | Chapter – 4 | Short Notes Series PDF

Phylum Arthropoda: Arthropoda is the largest phylum with about nine lakh species. They may be aquatic, terrestrial or even parasitic. They have jointed appendages and a chitinous exoskeleton.

Characteristics of Phylum Arthropoda

  • Insectsarachnids and crustaceans are members of the largest category of creatures on the planet: arthropods.
  • Arthropods have hard, external shells called “exoskeletons,” segmented bodies and jointed legs.
  • Some familiar examples are prawns, butterflies, houseflies, spiders, scorpions and crabs and some
  • They exhibit organ-system level of organisation.
  • They are bilaterally symmetrical, triploblastic, segmented and coelomate The coelomic cavity is blood-filled.
  • The body of arthropods is covered by chitinous The body consists of head, thorax and abdomen.
  • There is an open circulatory system, and so the blood does not flow in well defined blood vessels.
  • Respiratory organs are gills, book gills, book lungs or tracheal system.
  • Sensory organs like antennae, eyes (compound and simple), statocysts or balance organs are present.
  • Excretion takes place through malpighian tubules.
  • They are mostly dioecious.
  • Fertilisation is usually internal.
  • They are mostly oviparous.
  • Development may be direct or indirect.

Classification of Phylum Arthropoda

The classification of phylum arthropoda are as follows:

Crustacea

  1. They are aquatic, terrestrial, or parasitic.

  2. The head is fused with the thorax region known as the cephalothorax.

  3. Respiration occurs through gills or general body surface.

  4. The body is covered by a single large carapace.

  5. They possess two pairs of antennae and five pairs of appendages.

  6. They excrete through green glands or antennal glands.

  7. They have a pair of compound eyes and gonopores.

  8. Development is indirect. Larval stage is present.

  9. Eg., Daphnia, Palaemon

The subphylum Crustacea is divided into six classes-

  • Branchiopoda

  • Remipedia

  • Chephlocarida

  • Maxillopoda

  • Ostracoda

  • Malacostraca

Myriapoda

  1. These are mostly terrestrial.

  2. The body is elongated with numerous segments.

  3. The head is provided with antennae, two pairs of jaws, and a pair of simple eyes.

  4. They contain numerous legs.

  5. The upper lip of the mouth contains epistome and labrum, and the lower lip contains a pair of maxillae.

  6. A pair of mandibles is present inside the mouth.

  7. They respire by trachea and excretion occurs by Malpighian tubules.

  8. Eg., Julus, Scolopendra

The subphylum Myriapoda is divided into the following classes:

  • Chilopoda

  • Diplopoda

  • Pauropoda

  • Symphyla

Hexapoda

  1. They are mostly terrestrial.

  2. The body is differentiated into head, thorax, and abdomen.

  3. Head bears a pre-segmental acron.

  4. The thorax is divided into three segments.

  5. The abdomen has 7-11 segments.

  6. They have three pair of appendages.

  7. It has a pair of compound eyes

  8. They respire through gills and trachea.

  9. Malpighian tubules are the excretory organ.

  10. Development is indirect, and the larval stage is present.

  11. Eg., Tabernus, Mosquitoes, Ants.

The subphylum Hexapoda is divided into two classes:

  • Insecta

  • Entognatha

Chelicerata

  1. They are mostly found on land.

  2. The body is differentiated into cephalothorax and abdomen.

  3. Antennae are absent.

  4. The abdomen is divided into 13 segments.

  5. It has four pairs of interior appendages.

  6. They respire through trachea or gills.

  7. The Malpighian tubules help in excretion.

  8. Eg., Aramea, Limulus

The subphylum Chelicerata is divided into the following classes:

  • Arachnida

  • Merostomata

  • Pycnogonida

Onychophora

  1. These are small-sized, terrestrial arthropods.

  2. The body is divided into segments.

  3. Excretion occurs through nephridia.

  4. They respire through the trachea.

  5. Eg., Paripatus

Trilobitomorpha

  1. These are primitive arthropods and are extinct.

  2. They were found in abundance during the Paleozoic era.

  3. The body was divided into three lobes- one median and two lateral lobes.

  4. Head bore a pair of compound eyes and a pair of antennae.

  5. There was no structural differentiation of the body parts.

  6. The body was divided into head, thorax and pygidium.

  7. Appendages are biramous.

The subphylum had only one class- Trilobita


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