Phylum Arthropoda: Characteristics & Classification

Phylum Arthropoda is the largest phylum in the animal kingdom. The animals in this phylum have three parts to their bodies: a segmented body, an exoskeleton, and jointed appendages.

• Phylum Arthropoda is a type of phylum that may be aquatic, terrestrial or even parasitic. 
• These animals have exoskeletons with a cuticle made of chitin.

The term Arthropods is derived from the Greek words "arthron" (joint) and "podos" (foot or leg), which collectively mean "jointed leg." 

• The animals in this phylum have the ability to survive in every habitat.
• Phylum Arthropoda undergoes different stages of mouling in order for their growth.
• Insects, bees, shrimps, centipedes, millipedes, and other animals are included in this phylum.

Key Terms: Phylum Arthropoda, Animals Kingdom, Parasitic, Habitat, Trilobitomorpha, Chelicerata, Crustacea, Myriapoda, Classification of Phylum Arthropoda, Hexapoda, Aquatic Animals, Terrestrial Animals

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Classification of Phylum Arthropoda

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Arthropoda is subdivided into five subphyla. The following is a description of the five subphylums of phylum arthropoda:

Trilobitomorpha

The characteristics of Trilobitomorpha are as follows:

• Trilobitomorpha are the earliest form of arthropods.
• They are no longer extant.
• These species of animals have three lobes on their body: one median and two lateral lobes.
• Their body is divided into three sections: the head, the abdomen, and the pygidium.
• There are two antennas and compound eyes.
• Trilobita was the only class in this subphylum.

Chelicerata

The characteristics of Chelicerata are as follows:

• Chelicerata are mostly found on land.
• The body is divided into two parts: the cephalothorax and the abdomen.
• Antennae are missing in these species.
• The abdomen is divided into 13 segments.
• In chelicerata, respiration occurs through the trachea or gills.
• Malpighian tubules are found in the excretory organ.

The Chelicerata subphylum is further subdivided into the following classes:

• Arachnida
• Merostomata
• Pycnogonida

Myriapoda

The characteristics of Myriapoda are as follows:

• Myriapoda are mostly terrestrial in nature.
• Their body is long and slender, with numerous segments.
• They have two antennae and two simple eyes.
• These species have a lot of legs.
• Epistome and labrum are located on the upper lip of the mouth.
• A pair of maxillae are located on the lower lip.
• The presence of two mandibles inside the mouth.
• The trachea is responsible for respiration in myriapoda
• Malpighian tubules are responsible for excretion.

The Myriapoda subphylum is further subdivided into the following classes:

• Chilopoda
• Diplopoda
• Pauropoda
• Symphyla

Crustacea

The characteristics of Crustacea are as follows:

• Crustacea are mostly aquatic, with a few parasitic species thrown in for good measure.
• The body is divided into two parts: the cephalothorax (head + thorax) and the abdomen.
• Respiration occurs through the body's surface or through the gills.
• They have two pairs of antennae and compound eyes.
• Coxal glands, green glands, and antennary glands are examples of excretory organs.
• Crustacea demonstrate indirect development.

​Crustacea is further subdivided into six classes. They are as follows:

• Branchiopoda
• Remipedia
• Cephalocarida
• Maxillopoda
• Ostracoda
• Malacostraca

Hexapoda

The characteristics of Hexapoda are as follows:

• Hexapoda have the greatest diversity of species which can be found in a variety of habitats.
• The body is divided into three sections: the head, the thorax, and the abdomen.
• They have three pairs of appendages and two compound eyes.
• The thorax is divided into three sections in hexapoda.
• Respiration is accomplished through the use of the lungs or the trachea.
• Malpighian tubules are responsible for excretion.
• They demonstrate indirect development.

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Arthropoda Characteristics

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Some important characteristics of phylum arthropoda are as follows:

• Phylum Arthropoda contains roughly 80% of all animal species in the animal kingdom.
• They are coelomate animals that are bilaterally symmetrical and triploblastic.
• Organisms have a chitinous exoskeleton covering their bodies.
• It is divided into three distinct parts: the head, the thorax, and the abdomen. 
• In some cases, the head and thorax are fused, resulting in a cephalothorax. 
• They have a body that is segmented on the outside.

Phylum Arthropoda has an open circulatory system where blood flows in the haemocoel, which is colourless blood (hemolymph). They are made up of a dorsal heart.

• Different arthropods have different respiratory organs. 
• Respiration occurs through gills in aquatic forms and through book lungs or trachea in terrestrial forms.
• The double ventral nerve cord that runs along the ventral body wall forms the nervous system. 

Each segment has a segmental ganglia. The excretory structures in most arthropods are the Malpighian tubules or green glands.

• Sensory organs in arthropods include antennae, eyes (compound and simple), statocysts, and balancing organs.
• They demonstrate sexual reproduction and fertilisation occur internally. 
• With the larval stage, development can be direct or indirect. 
• Parthenogenesis occurs in some arthropods, such as honey bee drones.

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Examples of Phylum Arthropoda

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Some common examples of Phylum Arthropoda are as follows:

Palaemon

The characteristics of Palaemon are as follows:

• Palaemon are found in freshwater streams, rivers, lakes, and ponds.
• They are bilaterally symmetrical and elongated.
• The body is split into two parts: the cephalothorax and the abdomen.
• Shrimp and Prawns are common examples of Palaemon.

The divisions of Palaemon are as follows:

• Kingdom: Animalia
• Phylum: Arthropoda
• Subphylum: Crustacea
• Class: Malacostraca
• Order: Decapoda
• Family: Palaemonidae
• Genus: Palaemon

Scolopendra

The characteristics of Scolopendra are as follows:

• Scolopendra is found in burrows, crevices, logs of wood, and fallen leaves. 
• They are nocturnal species and live in damp areas.
• They are elongated and flattened dorsoventrally. 
• The body is divided into two sections: the head and the trunk.
• The digestive or alimentary system includes the alimentary canal and digestive glands.
• Centipede is a common example of Scolopendra.

The divisions of Scolopendra are as follows:

• Kingdom: Animalia
• Phylum: Arthropoda
• Subphylum: Myriapoda
• Class: Chilopoda
• Order: Scolopendromorpha
• Family: Scolopendridae
• Genus: Scolopendra

Periplaneta

The characteristics of Periplaneta are as follows:

• Periplaneta are omnivorous nocturnal scavengers. 
• They prefer dark, warm kitchen corners, godowns, underground drains, and places with food and humid atmospheres.
• They are flattened dorsoventrally, segmented, elongated, and reddish-brown in colour. 
• The body is divided into three sections: the head, the thorax, and the abdomen.
• The cockroach's exoskeleton is made of chitin and is jointed.

They have spiracles (respiratory openings) on the lateral sides of the thorax and abdomen segments, which facilitate gas exchange.

• Periplaneta has well-developed compound eyes.
• They have long antennae that allow them to move in the dark.
• The cockroach is a common example of this category.

The divisions of Periplaneta are as follows:

• Kingdom: Animalia
• Phylum: Arthropoda
• Subphylum: Hexapoda
• Class: Insecta
• Order: Blattodea
• Family: Blattidae
• Genus: Periplaneta

Brachyura

The characteristics of Brachyura are as follows:

• Brachyura includes a hard carapace, which covers the head and thorax dorsally.
• The ventral boundary between the head and thorax is clearly defined.
• Only the last five segments of the thorax are readily visible.
• The attachment of the thoracic legs to the exoskeleton is clearly apparent.
• It consists of one pair of legs on each of these last five thoracic segments. 
• The first pair is modified as chelipeds, or claws, while the remaining four pairs are adapted for walking and the last pair for swimming.
• Crab is a common example of Brachyura.

The divisions of Brachyura are as follows:

• Kingdom: Animalia
• Phylum: Arthropoda
• Subphylum: Mandibulata
• Class: Crustacea
• Order: Decapods
• Family: Brachyura
• Genus: Cancer

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Things to Remember

• Arthropoda is the most diverse phylum, with approximately nine lakh species.
• They can be aquatic, terrestrial, or even parasitic in nature. 
• The animal species in this category of phylum have chitinous exoskeletons and appendages with joints.
• This phylum contains several large classes, including the class Insecta, which accounts for a large proportion of all species on the planet. 
• There are six subphylum in Phylum Arthropoda, which are: Crustacea, Myriapoda, Hexapoda, Chelicerata and Trilobitomorpha.

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