Phylum Arthropoda: Arthropoda is the largest phylum in the animal kingdom that can survive any condition and can live on land, water, or as parasites. The Arthropoda characteristics include having jointed appendages, segmented bodies and a chitinous exoskeleton structure which renders them great flexibility and mobility. These body structure also helps the organism in protecting itself from predators.

Among the Arthropoda phylum, the Insecta class covers a large portion of the species in the world. Cockroaches, lobsters and mosquitoes are some examples of Arthropoda. Students can refer to this article to know which other animals form a part of this phylum. Also, get details on the history of the phylum and the various ways the members of the phylum are classified.

Phylum Arthropoda Definition

Phylum Arthropoda is the largest Phylum of the animal kingdom. The body of the animals of this Phylum consists of three divisions: a segmented body, an exoskeleton made up of chitin, and jointed appendages. The structure of the exoskeleton keeps the animals flexible, mobile, and well protected. Arthropods may live on land, on water. They may be parasites as well. This Phylum includes animals like insects, bees, shrimps, centipedes, millipedes, crabs, spiders, lobsters, etc.

The word Arthropod is derived from the Greek word “arthron”, which means “joint”, and “podos” which means “foot” or “leg”, which collectively means “jointed leg”.

Fig: Examples of Arthropoda

History of Phylum Arthropoda

The origin of arthropods is very ancient, more than 500 million years ago. The most ancient arthropod fossil appeared in the Cambrian period 541 million to 485.4 million years ago, represented by trilobites, merostomes, and crustaceans. The trilobites were some of the earliest Arthropods shown in this fossil from the Devonian Period 419.2 million to 358.9 million years ago. Arthropods are present in large numbers and still evolving.

Fig. Trilobite Fossil

Phylum Arthropoda Characteristics

1. This is the largest Phylum in the animal kingdom. 
2. Phylum Arthropoda consists of about 80% of all animal species in the animal kingdom.
3. They are bilaterally symmetrical, triploblastic, coelomate animals.
4. The body covering of organisms is in the form of a chitinous exoskeleton. 
5. It is divided into three distinguished parts: head, thorax, and abdomen. In some cases, the head is fused with the thorax and is called a cephalothorax. They have an externally segmented body.
6. They contain an open circulatory system, the blood flows in the haemocoel, and they contain colorless blood (haemolymph). They consist of a dorsal heart.
7. The respiratory organ differs in different arthropods. In aquatic forms, respiration occurs through gills, and in terrestrial forms, respiration occurs through book lungs or tracheae.
8. The nervous system arises from the double ventral nerve cord, which extends along the ventral body wall. It bears segmental ganglia in each segment. 
9. In most arthropods, the excretory structures are the Malpighian tubules or green glands.
10. Arthropods have sensory organs like antennae, eyes (compound and simple), statocysts, or balancing organs.
11. Arthropods can survive in any habitat.
12. They show sexual reproduction. Sexes are separate, and fertilization is internal. The development is direct or indirect with the larval stage.  Some arthropods, like drones of honey bees, undergo Parthenogenesis.
13. Examples:
    a. Economically important insects-Apis, Bombyx, Laccifer 
    b. Vector – Anopheles, Culex, Aedes.
    c. Gregarious pest – Locusta (Locust). 
    d. Living fossil – Limulus (King crab).

Fig: Malpighian Tubules

Arthropoda Classes

The phylum Arthropoda is divided into five sub-phylum. The description of the five subphylums are given below:

Fig: Classification of Phylum Arthropoda

I. Trilobitomorpha

• They are primitive arthropods.
• They are extinct.
• They were commonly found during the Paleozoic era.
• Their bodies are divided into three lobes: one median and two lateral lobes.
• Their bodies are divided into head, abdomen and pygidium.
• A pair of antenna and compound eyes are present.
• They have biramous appendages.
• This subphylum had only one class- Trilobita

II. Chelicerata

a. They are mostly present on the land.
b. The body is divided into cephalothorax and abdomen.
c. Absence of antennae.
d. The abdomen contains 13 segments.
e. The respiration takes place through the trachea or gills.
f. The excretory organ is Malpighian tubules.
g. Examples: Aramea, Limulus, etc.

The subphylum Chelicerata is again divided into the following classes:
1. Arachnida
2. Merostomata
3. Pycnogonida

III. Myriapoda

a. They are mostly terrestrial.
b. Their body is elongated with many segments.
c. A pair of antennae,  two pairs of jaws and simple eyes are present.
d. They contain many legs.
e. The upper lip of the mouth possesses epistome and labrum.
f. The lower lip possesses a pair of maxillae.
g. Presence of a pair of mandibles inside the mouth.
h. The respiration takes place by the trachea.
i. The excretion occurs by Malpighian tubules.
j. Examples: Julus, Scolopendra, etc.

The subphylum Myriapoda is again divided into the following classes:
1. Chilopoda
2. Diplopoda
3. Pauropoda
4. Symphyla

IV. Crustacea

a. They are mostly aquatic; some are parasitic. They can live on land as well
b. The body is divided into cephalothorax (head + thorax) and abdomen.
c. Respiration takes place by body surface or by gills.
d. They have two pairs of antennae and a pair of compound eyes.
e. The excretory organs are coxal glands or green glands, or antennary glands.
f. They show indirect development.
h. They have five pairs of appendages

Examples: Palaeman (Prawn), Macrobrachium (Prawn), Daphnia, Cancer (Crab), Palinurus (Lobster), etc.

The subphylum Crustacea is further divided into six classes. These are:
1. Branchiopoda
2. Remipedia
3. Cephalocarida
4. Maxillopoda
5. Ostracoda
6. Malacostraca

V. Hexapoda

a. They contain the largest number of species.
b. These are found in all types of habitats but they are mostly terrestrial.
c. The body is divided into the head, thorax, and abdomen.
d. They possess three pairs of appendages.
e. They have a pair of compound eyes.
f. The thorax contains three segments.
g. Respiration takes place by book lungs or trachea.
h. Excretion occurs by Malpighian tubules.
i. They show indirect development.
j. Examples: Periplaneta (Cockroach), Musca (Housefly), Mosquitoes, Butterflies, Ants, Bees, Wasps, Termites, etc.

The subphylum Hexapoda is again divided into two classes:
1. Insecta
2. Entognatha

Examples of Arthropoda Phylum

The examples of Phylum Arthropoda are mentioned below:

Palaemon (Shrimp)

1. The systematic position of Palaemon is –
   Kingdom: Animalia
   Phylum: Arthropoda
   Subphylum: Crustacea
   Class: Malacostraca
   Order: Decapoda
   Family: Palaemonidae
   Genus: Palaemon

2. They are found in freshwater streams, rivers, lakes and ponds.

3. They are elongated, bilaterally symmetrical.

4. The body is divided into cephalothorax and abdomen.

Fig: Palaemon (Shrimp)

Scolopendra (Centipede)

1. The systematic position of Scolopendra is –
   Kingdom: Animalia
   Phylum: Arthropoda
   Subphylum: Myriapoda
   Class: Chilopoda
   Order: Scolopendromorpha
   Family: Scolopendridae
   Genus: Scolopendra

2. These are found in burrows, crevices, logs of wood and fallen leaves. They are nocturnal and found in damp places.

3. They are elongated and dorsoventrally flat­tened. The body is divided into the head and trunk.

4. The digestive or alimentary system of the Centipede in­cludes alimentary canal and digestive glands

Fig: Scolopendra (Centipede)

Periplaneta (Cockroach)

1. The systematic position of Periplaneta is –
   Kingdom: Animalia
   Phylum: Arthropoda
   Subphylum: Hexapoda
   Class: Insecta
   Order: Blattodea
   Family: Blattidae
   Genus: Periplaneta

2. They are common nocturnal, omnivorous scavengers. They prefer dark warm corners of the kitchen, godowns, underground drains, and places where food and humid atmospheres are available.

3. They are dorsoventrally flattened, segmented, elongated and reddish-brown in colour. The body is divided into the head, thorax, and abdomen.

4. The exoskeleton of cockroach is made of chitin and jointed.

5. They have spiracles (respiratory openings) on the lateral side of the segments of the thorax and abdomen. This helps in the exchange of gases.

6. They contain well-developed compound eyes.

7. They have long antennas to enable the animal to move in the dark.

Fig: Periplaneta (Cockroach)

Economic Importance of Phylum Arthropoda

Phylum Arthropoda is very important for a healthy ecosystem. Some of the importance of Phylum Arthropoda are mentioned below:

1. Pollination: Insects help in the pollination of flowers.
2. Soil fertility: Organisms of this Phylum like ants, beetles, and larvae burrow the soil, increasing soil fertility.
3. Nutrient for plants: Ants and termites enrich the soil, providing nutrients to the plant.
4. Biological Control: As members of this Phylum are predators, which help in the biological control of pests.
5. Silk: Silkmoth provides commercial silk, which is used in the fabric industry.
6. Honey: The honey bee produces honey.
7. Dyes: Lac insects are used to prepare many dyes.
8. Food: Some Arthropods, like crabs, prawns, are served as food.
9. Medicines: They are used in many medicines. For example, the blood of Blister Beetle is used to make Cantharidine.
10. Scientific Research: They are used in scientific research in laboratories.

Interesting Facts About Arthropoda

a. The biggest arthropod is Coconut Crabs.

Fig: Coconut Crabs

b. The tantulocarid stygotantulus stocki s the smallest arthropod.
c. Cockroach can live up to 9 days without its head.

Summary of Arthropoda Characteristics

Phylum Arthropoda is the largest Phylum of invertebrates. Arthropods have an ancient history, and many organisms in this Phylum are insects; they also include spiders, centipedes, and crustaceans. The body of Arthropoda is divided into three parts: a segmented body, a hard exoskeleton, and jointed appendages.

The Arthropoda is divided into five sub-phylum. Among the five sub-phylum, the sub-phylum Trilobitomorpha is extinct, and the sub-phylum Hexapoda contain the largest species. This phylum consists of various large classes. They possess the ability to survive in every habitat.

FAQs on Phylum Arthropoda

We have provided some frequently asked questions here about Phylum Arthropoda:

Q.1: What organisms are present in the Phylum Arthropoda?
Ans: The organisms present in the Phylum Arthropoda are prawns, scorpions, crabs, spiders, lobsters, ants, cockroaches, honeybees, etc.

Q.2: What is the scientific name of Cockroach?
Ans: The scientific name of Cockroach is Periplaneta americana.

Q.3: Why is the name Arthropods given?
Ans: The word Arthropod is derived from the Greek word “arthron”, which means “joint”, and podos which means “foot” or “leg”, which collectively means “jointed leg”.

Q.4: Which class do honey bees belong to?
Ans: The honey bees belong to the class Insecta.

Q.5: Why is Phylum Arthropoda known as the largest Phylum?
Ans:The Phylum Arthropoda is known as the largest Phylum because it includes around 80% of species of the animal kingdom.

Q.6: What are the five characteristics of Phylum Arthropoda?
Ans: 1. This is the largest Phylum in the animal kingdom.
2. Phylum Arthropoda consists of about 80% of all animal species in the animal kingdom.
3. They are bilaterally symmetrical, triploblastic, coelomate animals.
4. The body covering is in the form of a chitinous exoskeleton. 
5. It is divided into three distinguished parts: head, thorax, and abdomen. In some cases, the head is fused with the thorax and is called a cephalothorax. They have an externally segmented body.

Q.7: How are Arthropodas classified?
Ans: Animals belonging to the Arthropoda phylum are classified into Crustacea, Myriapoda, Hexapoda, Chelicerata, Onychophora and Trilobitomorpha.

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