Definition of 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 the 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 their 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 Arthropod 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 excrete waste through coaxial glands, and the terrestrials use malpighian tubules to excrete.
Phylum Arthropoda shows sexual dimorphism that is either internal or external.
These animals are unisexual.
With the help of the 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, the crustacea can respire through the trachea and gills.
Their head is merged with the thorax, and the body part is referred to as cephalothorax.
This kind of arthropod 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-
Remipedia
Branchiopoda
Maxillopoda
Cephalocarida
Malacostraca
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 the malpighian tubule.
They possess four pairs or eight interior appendages.
Example: sea spiders, Limulus etc.
Chelicerata has Three Sub-Categories-
Pycnogonida
Merostomata
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 are 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-
Chilopoda
Symphyla
Pauropoda
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:
Entognatha
Insecta
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Onychophora and its characteristics
They reside on the land.
They are smaller in size.
Their body is divided into segments.
The process of excretion takes place through nephridia.
They have a trachea for respiration.
Example- Peripatus, velvet worm, etc.
Onychophora has one class only - Udeonychophora.
Trilobitomorpha and its characteristics
These were the first arthropods to exist. However, they are now extinct.
They were abundant during the Palaeozoic era.
Their body was segmented into three lobes- two lateral and one median lobe.
Their head had a pair of antennae and compound eyes.
The structural differentiation of the body parts was not present.
Their body was divided into head, thorax and pygidium (a terminal segment or hind body part of annelids).
Appendages were biramous(divided into two).
Examples- planktons, kainella meridionalis, Incaicabishopi, etc.
Trilobitomorpha had only a single class- Trilobita.
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FAQs on Phylum Arthropoda
1. What does the term Arthropod mean?
The term arthropod means jointed legs. Through arthropods description, it is notable that the jointed leg is one of the most common features of phylum Arthropoda. Plus, they have an exoskeleton and a segmented body along with a joint pair of appendages. All arthropods come into a phylum called arthropods. They are distinguished by the presence of an exoskeleton made of chitin, jointed limbs and often mineralized in calcium carbonate. The body plan of the arthropod consists of segments with each side having a jointed limb.
2. What is an Arthropod?
An arthropod is an animal species that comes under the phylum Arthropoda. With some distinctive features, arthropods are classified into four categories. These categories are- Crustacea, Chelicerata, Myriapoda and Hexapoda. Arthropods are bilaterally symmetrical and contain an external skeleton. They undergo a process called moulting for their proper growth and development. In this process, they shed their skin or exoskeleton and regenerate a new one. Some arthropods have wings for flying purposes. This phylum is the largest in the animal kingdom having more than 10 million diverse species.
3. What are the Examples of Arthropods?
Scorpions, crabs, centipedes, lobsters, ants, mosquitoes, etc. are common examples of Arthropods. However, the animal kingdom is further classified into four categories.
Crustacea- These arthropods can be found on both land and water. Examples- woodlice, shrimp, etc.
Chelicerata- They are mostly terrestrial. Their body is divided between the abdomen and cephalothorax. Examples- Limulus, sea spiders.
Myriapoda- They reside on the land. Their body parts segments are easily visible. Examples- Pauropoda, millipedes, Symphyla, etc.
Hexapoda- Mostly found on land. Their body has three segments and possesses six appendages. Examples- Insects, springtail, diplura.
4. What are some features of arthropods?
The features of arthropods are as follows-
The body of an Arthropod is bilaterally symmetrical, triploblastic and segmented.
They show the organ system level of the organization.
Their body is divided into head, abdomen and thorax.
They have jointed legs for locomotion.
Their coelomic cavity has blood.
Arthropods have an open circulatory system.
They have a developed digestive system.
Respiration takes place through their body surface.
They contain sensory organs such as simple and compound eyes, hairs, statocysts, and auditory organs.
They are unisexual. And the fertilization takes place in both ways- internal and external.
5. How did arthropods evolve?
Arthropods have evolved to the same root as annelids. The three main categories of arthropods- the Crustacea, the Insecta and the Chelicerata have individually developed from a common ancestor. Scientists have only a bit of information about the ancestors of arthropods. The Arthropod ancestors might have a resemblance to Onychophora like Peripatus (animal having appendages and trachea like Arthropodaand body wall and an excretory system like annelids). Factors like an exoskeleton, waxy cuticles, jointed limbs are evolved from Arthropods ancestors helps newly evolved arthropods to survive in the harsh climate.
