Arthropoda

Arthropods, a group of animals, got their name from the Greek words “arthron” (meaning joint) and “pous” (meaning foot). They are found in many places like land, sea, and air. There are a lot of different types of arthropods – in fact, there are one million known species, making them the biggest group of animals on Earth. They make up more than 80% of all animal species, and two-thirds of the named species on our planet. Among all these different types, insects are the most common in the animal kingdom.

Arthropods have a body structure with three layers, and their bodies are symmetrical on both sides. They also have segmented bodies with hard outer coverings made of a substance called chitin, and their limbs are made up of segments that can bend, which helps them move. These unique features are a big reason why arthropods have been so successful and able to adapt to different environments.

Evolutionary advancement over annelids

Arthropods are more advanced in evolution compared to annelids because they have certain special features like:

1. Putting their sensory organs and brain parts mostly in their head.
2. Having parts like legs and arms that can bend and move.
3. Muscles that look striped.
4. Having a tough outer covering made of a hard material called chitin.
5. Having special breathing structures.

These changes make it easier for arthropods to talk with chemicals called pheromones and react well to what’s happening around them in their environment.

Habitat

Arthropods, like insects and spiders, can live in many different places like the ocean, lakes, and on land. They have bodies with parts like legs and claws that help them do different jobs, making them come in lots of different types. Spiders, for example, don’t have feelers. Arthropods look the same on both sides and have tough outer parts that are split into sections.

Metamerism and tagmata

One important thing to know about these creatures is that their bodies are divided into three parts: the head, thorax, and abdomen. Another interesting fact is that they have body segments and special parts that do different jobs. One cool thing they have are parts that work like levers and muscles to help them move, which is something new that evolved in the group of animals they belong to, called Arthropods.

Exoskeleton

Arthropods have a tough outer covering made of a substance called chitin, which helps protect them from drying out and from things that might harm them on the outside. They grow by getting rid of their old outer covering in a process called molting. Inside their bodies, there’s a space where important things like reproductive organs and waste removal parts are located, and it’s not very big. Another part inside them is filled with a liquid called hemolymph, which comes from when they were just tiny embryos and their bodies were forming.

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Functional systems

1. The digestive system has three parts: the foregut, midgut, and hindgut. Each part does a different job.
2. Some animals have special ways to breathe depending on where they live. They might have gills if they live in water, or tracheae and book lungs if they live on land.
3. The blood system in these animals is different. They have a heart in their back, and their blood has a special pigment called haemocyanin. This is true for creatures like spiders and crabs.
4. Getting rid of waste in their bodies is done differently too. Land animals use something called Malpighian tubules, while water animals use coxal glands and green glands.
5. These animals also have a nervous system. They have a nerve ring and a strong nerve cord on their belly. They also have good sense organs like antennas, simple eyes, compound eyes, and statocysts.

Reproduction and development

Most are unisexual with internal fertilisation and are oviparous. Development encompasses both direct and indirect pathways, often involving metamorphosis. Larval stages frequently differ from adults in habitat and feeding habits.

Examples

• Economically important insects – Apis (honeybee), Bombyx (silkworm), Laccifer (lac insect)
• Vectors – Anopheles, Culex and Aedes (mosquitoes)
• Gregarious pest – Locusta (locust)
• Living fossil – Limulus (king crab)

Classification

The classification of Phylum Arthropoda is outlined as follows:

• Class Xiphosura: This class comprises creatures such as the horseshoe crab (Limulus), which is recognized for its distinct appearance and lineage.
• Class Arachnida: Arachnids, characterized by their eight-legged form, populate this class. Examples include Palamnaeus, Aranea (garden spider), and Sarcoptes (itch mite).
• Class Crustacea: Creatures falling under this class are predominantly aquatic and exhibit a wide range of forms. Examples encompass Palaemon (Macrobrachium), a freshwater prawn, Balanus (rock barnacle), Sacculina (root-headed barnacle, a parasite on crabs), Astacus (crayfish), Cancer (crab), and Daphnia (water flea).
• Class Chilopoda: Centipedes, with their elongated bodies and numerous legs, belong to this class. Scolopendra and Scutigera serve as representative examples.
• Class Diplopoda: Millipedes, distinct for their numerous legs and cylindrical bodies, are part of this class. Examples include Julus, Spirostreptus, and Spirobolus.
• Class Hexapoda or Insecta: The largest and most diverse class, Hexapoda, commonly known as insects, dominates the animal kingdom. Examples encompass Musca (house fly), Lepisma (silverfish), and Periplaneta (cockroach).

Summary

Arthropoda, a diverse and prolific phylum, thrives across land, sea, and air, housing over one million species and encompassing 80% of animal diversity. Its various classes, such as Insecta, showcase exceptional adaptations, from jointed appendages to specialized respiratory systems, underpinning their evolutionary success. Arthropods’ impact extends economically and ecologically, with species like honeybees, mosquitoes, and silkworms playing pivotal roles. Their innovative traits, including cephalization and protective exoskeletons, underscore their ability to conquer diverse habitats. As intricate ecosystems’ inhabitants, arthropods significantly contribute to Earth’s biodiversity and biological interactions.

FAQs on Arthropoda

What does the term Arthropoda mean?

Arthropoda is derived from the Greek words arthron (joint) and pous (foot), signifying jointed-legged organisms.

How diverse is the Arthropoda phylum?

Arthropoda is incredibly diverse, with over one million described species, constituting more than 80% of animal species and two-thirds of all named species on Earth.

What is the largest class within the Arthropoda phylum?

The largest class is Insecta, which comprises a vast array of insects and dominates the animal kingdom in terms of diversity and numbers.

What are some key anatomical features of arthropods?

Arthropods possess jointed appendages, a chitinous exoskeleton, and heteronomous metamerism, contributing to their adaptability and success.

How do arthropods compare to annelids in terms of evolution?

Arthropods have evolved advanced features like cephalization, jointed appendages, striated muscles, and a protective exoskeleton, giving them an edge over annelids.

What are some examples of economically important arthropods?

Economically significant arthropods include honeybees (Apis), silkworms (Bombyx), and disease vectors like mosquitoes (Anopheles, Culex, Aedes).

Do arthropods inhabit diverse habitats?

Arthropods showcase remarkable habitat adaptability, thriving in marine, freshwater, and terrestrial ecosystems due to their segmented bodies and specialized appendages.

What is the significance of jointed appendages in arthropods?

Jointed appendages act as lever systems, offering mechanical advantage for locomotion and various functions. They play a key role in the evolutionary success of arthropods.

How do arthropods reproduce and develop?

Most arthropods are unisexual with internal fertilization. They exhibit both direct and indirect development, with metamorphosis playing a crucial role in their life cycles.

What is the classification of Phylum Arthropoda?

Phylum Arthropoda is classified into classes including Xiphosura, Arachnida, Crustacea, Chilopoda, Diplopoda, and Hexapoda (Insecta), each showcasing unique characteristics and ecological roles.