Phylum Arthropoda

Phylum Arthropoda is the largest phylum in the Kingdom Animalia and it includes insects. Arthropoda makes up more than two-thirds of all known species worldwide. The phylum Arthropoda characteristics include jointed appendages, a well-organized body structure with a segmented design, and a tough exoskeleton made of chitin. The Arthropoda body is divided into three sections: head, thorax, and abdomen.

The Phylum Arthropoda examples include insects such as ants, and butterflies arachnids like spiders and scorpions, crustaceans such as crabs, lobsters, and shrimp, as well as myriapods including centipedes and millipedes. In this article, we will cover the Phylum Arthropoda and its classification, and characteristics in detail.

Phylum Arthropoda

Phylum Arthropoda is the largest Phylum in Kingdom Animalia. It includes many different creatures like insects, spiders, crabs, and millipedes. They have jointed legs, hard outer shells, and bodies made of segments. Arthropods can be found at all places including ground and ocean, and they are important for keeping ecosystems balanced.

Phylum Arthropoda Characteristics

Some of the distinguishing features of Arthropoda are given below:

• The body consists of the head, thorax, and abdomen. There is a distinct head.
• They have jointed appendages.
• The body is covered with a thick, touch and non-living chitinous cuticle, which forms the exoskeleton. 
• The true coelom is greatly reduced in adults, and is only represented by the cavities of the reproductive and excretory organs. The body cavity is a haemocoel viz., cavity filled with blood.
• Digestive tract is complete. The alimentary canal consists of the stomodaeum (foregut), mesenteron (midgut), and proctodaeum (hindgut).
• The blood vascular system is of open type viz, Blood does not flow in definite vessels. There are present irregular spaces, known as lacunae or sinuses, filled with blood to form the haemocoel.
• The respiratory organs are gills or book gills in aquatic forms and tracheae or book-lungs in terrestrial forms. The exchange of gases is also carried on by the general body surface in some forms.
• The excretory organs are either green glands or Malpighian tubules. In some forms, coxal glands are excretory organs.
• The annelids type of nervous system is present, viz., it consist of a nerve ring and a double ganglionated ventral nerve cord.
• In many arthropods, compound eyes are present, in which mosaic vision is developed.
• An important feature of the arthropods is the complete absence of the cilia.
• Endocrine glands are absent.
• Sexes are separate and the sexual dimorphism is observed in many forms. The development of the animal may involve metamorphosis.
• Parental care is often seen in many arthropods.
• Fertilization is usually internal, oviparous, or ovoviviparous.

Classification of Phylum Arthropoda

The Phylum Arthropoda involves 7 classes which are discussed below:

Class 1 Onychophora

• The body is elongated, segmented, and covered with a thin cuticle. 
• Peripatus is an important example of the class Onychophora which has characters of phylum Annelida and Arthropoda. Hence it is called connecting link.
• Examples of Onychophora: Peripatus and Principapillatus

Class 2 Crustacea

• The body is divisible into cephalothorax (head+thorax) and abdomen. 
• Dorsally, the cephalothorax is covered by a thick exoskeleton carapace. 
• There are present two pairs of antennae and a pair of stalked compound eyes. 
• Respiration is carried out either by body surface or by gills.
• Example of Crustacea: Crab, Daphnia, Shrimp

Class 3 Insecta 

• The body is divisible into the distinct head, thorax, and abdomen.
• The abdomen lacks appendages, the head has a pair of antennae and mouth parts and the thorax has three pairs of legs and two pairs of wings.
• Respiration by tracheae.
• Example of Insecta: Grasshopper, Butterfly, and Honey bee

Class 4 Arachnida 

• Body divisible into cephalothorax and abdomen.
• Antennae and true jaws are absent. 
• Respiration by tracheae, book-lungs, or book gills. 
• Example of Arachnida: Spider, Scorpions, and Mites.

Class 5 Merostomata

• Limulus, (the king or Horseshoe crab) is a good example of class Merostomata which respires through book gills. The king’s crabs are called living fossils. A living fossil is a living animal of ancient origin with many primitive characters.

Class 6 Chilopoda 

• The body is divisible into the head and trunk. 
• The first pair of legs are modified into poison claws.
• There is a single pair of antennae. 
• Respiration occurs by tracheae. 
• Excretion takes place by Malpighian tubules,
• Example of Chilopoda: Centipede

Class 7 Diplopoda 

• Body is divisible into the head, thorax, and abdomen. 
• There is a single pair of antennae.
• Respiration occurs by tracheae. 
• Excretion takes place by Malpighian tubules.
• Example of Diplopoda: Millipede

Chilopoda and Diplopoda were earlier included in a single class Myriopoda.

• The body is elongated and metamerically segmented with each segment having one or two pairs of legs. 
• Respiration by tracheae. Examples: Scolopendra (centipede), Julus (millepede).

Respiratory System of Phylum Arthropoda

Most of the arthropods that live on land have lungs and trachea as their respiratory organs. The trachea allows the air into the body through small holes. Aquatic arthropods have gills as their primary organ for respiration. Gills help them in the process of respiration in water. Gills are present on the skin of most arthropods that are further covered by an exoskeleton. Most insects have tracheae and book lungs, yet huge bugs (like tarantulas) and scorpions have lungs alone.

Circulation System of Phylum Arthropoda

The arthropods have open circulatory system. It consists of the dorsal heart and arteries which are in small numbers in insects and very extensive in large creatures like crabs. Blood is delivered into the tissue spaces called hemocoels by arteries. Small creatures like crustaceans and a few insects like larvae have hemoglobin in their blood just like humans. A changing number of matched openings are situated along the length of the heart and license blood to stream in when the valves are open.

Exoskeleton of Arthropoda

The material that forms the outer layer of the exoskeleton is chitin. It is a tough layer. The exoskeleton is a thickened area formed by the combination of chitin and some proteins. Commonly the mineral gems, essentially calcium carbonate, are stored among the chitin and protein particles in a cycle called biomineralization. The precious stones and filaments interpenetrate and support one another, the minerals providing the hardness and protection from pressure, while the chitin supplies the elasticity.

Nervous System of Phylum Arthropoda

There is a ventral and dorsal brain in the nervous system of arthropods. The nervous system in Arthropods is a ladder-like nervous system that contains a double chain along the ventral surface. It also consists of a nerve chord that is longitudinal from the extension of lateral nerves. The nervous system in arthropods is almost similar to annelid worms. The dorsal ganglia are enough bigger than the other ganglia to be known as a mind. The neuromuscular association of arthropods is very unique from that of vertebrates, in which one neuron supplies various muscle cells, together shaping a practical motor unit.

Digestive System of Phylum Arthropoda

Arthropods have all type of feeding creature like Herbivores, Carnivores, Parasites, filters, and detritus feeders. Normally, matched limbs around the mouth are utilized for gathering and taking care of food and are generally accomplished as per the specific eating routine of the creature. The front and back pieces of the intestinal system are fixed with the very skeletal material that is found outwardly of the body and that is shed with the remainder of the skeleton.

Excretory System of Phylum Arthropoda

Different types of arthropods possess different excretory systems. Organisms like arachnids have paired excretory organs. Myriapods, insects, and mites-like creatures have different excretory organs. They have Malpighian tubes open into the intestine. Loosing of water because of evaporation is a significant issue for terrestrial arthropods and a variety of safeguards against drying up have been developed. 

Reproduction System of Phylum Arthropoda

Different kinds of arthropods possess different types of reproduction. The different types of reproduction are Polyembryony, viviparity, and parthenogenesis. In arthropods, sperm are usually moved to the female inside fixed parcels known as spermatophores. This waterproof packet protects the sperm from the environment, preventing them from drying out on land or being diluted in water. Arthropod eggs are typically rich in the yolk, yet there are species whose eggs have a little yolk.

Senses in Arthropods of Phylum Arthropoda

The sense organs in arthropods are a specialization of an exoskeleton. Sense organs in arthropods include mouth parts, leg tips, peg-like projections, cones, pits, or slits. Changes in the pressure of the encompassing fingernail skin initiate the sensitive spots. For instance, the legs of bugs and scorpions have cuts in the exoskeleton that are covered by a layer to which a neuronal receptor is joined underneath.

Differences Between Annelids and Arthropods

The major difference between annelids and arthropods is given below:

Difference	Annelids	Arthropods
Body Structure	Segmented body with internal organs	Segmented body with chitinous exoskeleton
Respiratory System	Primarily rely on skin or gills for respiration	Possess diverse respiratory organs like gills, book lungs, or tracheal systems
Appendages	Lack jointed appendages	Have jointed appendages for movement
Circulatory System	Closed circulatory system with blood vessels	Open circulatory system with hemolymph
Reproductive Methods	Mostly monoecious, some dioecious	Mostly dioecious, with internal fertilization
Habitat	Found in diverse habitats like soil, freshwater, and marine environments	Inhabit a wide range of environments, including terrestrial, aquatic, and aerial habitats

Conclusion – Phylum Arthropoda

In conclusion, Phylum Arthropoda is the largest within the Animal Kingdom and has an immense diversity. Arthropods characteristics includes jointed appendages, segmented bodies, and a chitinous exoskeleton. Examples of phylum Arthropoda include ants, butterflies, spiders, crabs, and millipedes.

FAQs on Phylum Arthropoda

Define the Largest Phylum of Animalia.

Phylum Arthropoda- The Animals with Jointed Feet is the largest phylum of Arthropoda. The body consists of the head, thorax, and abdomen. There is a distinct head. They have jointed appendages.

What are the Five Main Classes of Arthropods?

Onychophora, Crustacea, Myriapoda, Insecta, and Arachnida are the main classes of Arthropoda.

Where do Most Arthropods Live?

Arthropods are found in virtually every known marine (ocean-based), freshwater, and terrestrial (land-based) ecosystem, and vary tremendously in their habitats, life histories, and dietary preferences.

What is the Study of Arthropods Called?

Arthropodology is known as the study of Arthropods.

Give Examples of Arthropods.

Examples of arthropods are lobsters, crabs, spiders, mites, insects, centipedes, and millipedes.

What are the Main Characteristics of Phylum Arthropoda?

The main characteristics of Phylum Arthropoda include jointed appendages, a segmented body with a chitinous exoskeleton, and distinct head, thorax, and abdomen regions.

What is Arthropoda Class 11?

Arthropoda is a classification referring to a diverse group of invertebrate animals with jointed legs and exoskeletons.

What is the Structure of the Arthropods?

Arthropods have a segmented body divided into head, thorax, and abdomen, with jointed appendages and a tough chitinous exoskeleton covering their bodies.