Phylum Arthropoda

Arthropoda defines the largest phylum among the animal kingdom, and it comes under the phylum Arthropoda. These animals have jointed appendages, a segmented body, and an exoskeleton structure covered with chitin. Due to the exoskeleton structure, these animals are flexible, mobile, and also well protected. 

Phylum Arthropoda can dwell in both water and land. Moreover, some of them are parasitic. These animals are used as the food source for various living beings.


Arthropods Examples:

Some familiar forms of arthropods are lobster, spider, centipedes, crab, millipedes, mites, cockroach, butterfly, mosquito, ants etc. 


General Characteristics of Arthropods

The Arthropods Characteristics are Listed Below-

  • The body of arthropods is bilaterally symmetrical.

  • These animals are triploblastic, and the body is segmented into head, thorax, and abdomen.

  • They have jointed appendages that help in movements.

  • The body cavity is filled with white coloured blood that is known as haemocoel.

  • The exoskeleton structure is hard and made of complex sugar, namely chitin.

  • Arthropoda species can be both terrestrial and aquatic.

  • These animals have compound eyes on theirs head, capable of mosaic vision.

  • Their nervous system is well-developed.

  • Their heads bear the brain and all the sensory organs such as antennae, hair, statocysts, and auditory organs.

  • One of the most important features of arthropods is their open circulatory system with arteries and dorsal heart.

  • In an Arthropoda diagram, the digestive tract is found with the mouth at one end and the anus at the opposite part of the body.

  • The aquatic arthropods excretes waste through coaxal glands, and the terrestrials use malpighian tubule to excrete.

  • Phylum Arthropoda shows sexual dimorphism that is either internal or external.

  • These animals are unisexual.

  • With the help of trachea or book lungs, the terrestrial forms perform respiration. Their aquatic type uses gills or the body surface to respire.


Classification of Arthropoda

There are 4 classes of arthropods that can be mostly found - Crustacea, Chelicerata, Myriapoda, and Hexapoda. However, two other classes of arthropods can also be derived – Trilobitomorpha, the extinct category and Onychophora.

Here are the classes of arthropods and characteristics of these classes mentioned separately.


Crustacea and its Characteristics:

  • This type of Phylum Arthropoda can be found in both land and water.

  • These can be parasitic as well.

  • Depending on their habitat, crustacea can respire through trachea and gills.

  • Their head is merged with the thorax, and the body part is referred as cephalothorax.

  • This kind of arthropods has ten appendages and two pairs of antennae.

  • A single carapace covers the entire body.

  • These arthropods possess gonopores and two compound eyes.

  • They excrete through antennal glands or green glands.

  • The larva stage is visible in their life cycle.

  • Example: prawns, crabs, woodlice, shrimp, etc.


The Crustacea can be Further Divided into Six Sub-Categories-

  1. Remipedia

  2. Branchiopoda

  3. Maxillopoda

  4. Cephalocarida

  5. Malacostraca

  6. Ostracoda


Chelicerata and its Characteristics:

  • They are terrestrial.

  • Antennae are not present.

  • Their body is divided between cephalothorax and abdomen that is segmented into thirteen parts.

  •  Chelicerata performs respiration through gills or trachea.

  • They excrete through malpighian tubule.

  • They possess four pairs or eight interior appendages.

  • Example: sea spiders, Limulus etc.


Chelicerata has Three Sub-Categories-

  1. Pycnogonida

  2. Merostomata

  3. Arachnida


Myriapoda and its Characteristics:

  • They primarily dwell on land.

  • Several segments are visible on their body.

  • Their head carries two simple eyes, antennae, and two pairs of jaws.

  • Inside their mouth, a pair of mandibles is visible.

  • Labrum and epistome are present in the upper lip, and the lower lip has two maxillae.

  • The trachea is their respiratory organ, and malpighian tubules help in excretion.

  • They have several legs.


Myriapoda is Classified into Four Sub-Categories-

  1. Chilopoda

  2. Symphyla

  3. Pauropoda

  4. Diplopoda


Hexapoda and its Characteristics:

  • They are mostly found on land.

  • Their body has three segments.

  • A pair of compound eyes and one pre-segmental Acron are present on the head.

  • The thorax is further segmented into three parts.

  • Their abdomen is divided into 7-11 segments.

  • They possess six appendages.

  • Hexapods respire through book lungs or trachea.

  • Malpighian tubules help them to excrete.

  • Example: cockroach, mosquito, fly, ant, wasp, etc.


Hexapoda has Two Sub-Classes:

  1. Entognatha

  2. Insecta

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FAQ (Frequently Asked Questions)

1. What does the term Arthropod mean?

Ans. The term arthropod means jointed legs. Through arthropods description, it is notable that jointed leg is one of the most common features of phylum Arthropoda.

2. What is an Arthropod?

Ans. An arthropod is an animal species that come under phylum Arthropoda. With some distinctive features, arthropods are classified into four categories.

3. What are the Examples of Arthropods?

Ans. Scorpions, crabs, centipedes, lobsters, ants, mosquitoes, etc. are common examples of Arthropods.