Arthropods are interesting creatures with jointed legs and tough exoskeletons made of chitin.

These animals include insects, spiders, and crabs. They make up about 84% of all known animal species.

Arthropods have evolved amazing sensory systems, like compound eyes and bristles. These help them navigate their environments.

They can live in water, on land, or in the air. Arthropods are great at adapting.

They are important in ecosystems and can also affect human health and agriculture.

Etymology of Arthropods

The term “arthropod” comes from Greek words. “Arthron” means joint, and “pous” or “pod” means foot. French zoologist Pierre André Latreille first coined the name. He used it to describe animals with jointed limbs.

Arthropods have jointed appendages. The term now covers many invertebrate species in the phylum Arthropoda. This includes insects, crustaceans like crabs and shrimp, and arachnids such as spiders and mites.

Arthropods have segmented bodies like the head, thorax, and abdomen. They have chitinous exoskeletons. They also have special structures like antennae, maxillae, and mandibles. They go through a moulting process where they shed an old exoskeleton to grow a new one.

Arthropods are diverse. They include terrestrial animals like centipedes and millipedes. They also include marine organisms like lobsters, crayfish, and barnacles. The term is established in biological sciences, showing the diversity and adaptation of these animals.

Phylum Arthropoda

Arthropods are invertebrates with jointed legs, segmented bodies, and an outer shell made of chitin. This shell is called an exoskeleton or cuticle. Arthropods shed their exoskeleton in a process called molting so they can grow.

These creatures have special body parts: a head, thorax, and abdomen. These parts differ among species. The phylum Arthropoda is split into several groups:

• Hexapoda (insects)
• Crustacea (crabs, shrimp, barnacles)
• Chelicerata (spiders, mites, horseshoe crabs)
• Myriapoda (centipedes, millipedes)

Each group has unique features. For example, crustaceans have swimmerets and insects have mandibles. The exoskeleton gives protection, support, and keeps water inside for land species.

Arthropods have advanced sensory systems. They use antennae, setae, and compound eyes to sense their surroundings. Marine crustaceans add calcium carbonate to their shells for extra strength.

These adaptations make arthropods very successful. Over 85% of all known animal species are arthropods.

Subphylum Classification

In arthropods, subphylum classification is based on features like body segments, jointed legs, and exoskeletons made of chitin and sometimes calcium carbonate.

Here’s a breakdown of different subphyla:

1. –Chelicerata–: Includes spiders, horseshoe crabs, and mites. They lack antennae and have chelicerae.
2. –Crustacea–: Includes crabs, shrimp, lobsters, and barnacles. They have two pairs of antennae, mandibles, maxillae, and swimmerets.
3. –Hexapoda–: Includes insects. Insects have three body parts: head, thorax, and abdomen. They undergo metamorphosis.
4. –Myriapoda–: Contains centipedes and millipedes.

These are terrestrial with many body segments and jointed appendages.

Arthropods are invertebrates with exoskeletons. They shed their exoskeletons through moulting. They have compound eyes and setae to sense their environment. Their bodies use haemolymph for circulation.

Insects make up the largest group within the phylum Arthropoda.

Terrestrial and marine arthropods have developed unique adaptations for their environments.

Latreille named this phylum which showcases vast animal species diversity.

Description and Characteristics

Segmentation

Arthropods have segmented bodies. These segments can be seen in their head, thorax, and abdomen.

Each segment has a specific function and includes legs, antennae, and setae.

Insects show clear segmentation with three main body parts: head, thorax, and abdomen.

Spiders have two main body segments. They are part of the chelicerates group.

Crustaceans, like crabs, shrimp, crayfish, and lobsters, have varied segmentation. Their jointed appendages are adapted for tasks like swimming and feeding.

The exoskeleton is made of chitin and sometimes strengthened with calcium carbonate. This provides support and protection. Moulting allows them to grow.

Segmentation helps arthropods adapt and develop specialized functions in different segments. This enables them to live in diverse places.

For example, barnacles and horseshoe crabs have unique adaptations but belong to the same phylum, Arthropoda.

Their jointed limbs help with movement in various environments, from land to water.

With about 85% of all known animal species, arthropods show that segmentation and development lead to success.

Exoskeleton

Arthropods have an outer shell called an exoskeleton. This exoskeleton offers support and protection. It is made of chitin mixed with proteins, and sometimes calcium carbonate. Acting like armor, it protects their body and internal organs.

The exoskeleton has segments and jointed parts like legs and antennae. These segments include the head, thorax, and abdomen. In crustaceans like crabs and shrimp, the exoskeleton has hard plates. Insects also have segmented bodies, which help them move.

Arthropods need to grow. They do this by moulting, which means shedding the old exoskeleton. After shedding, their new exoskeleton is soft and weak until it hardens. Crabs and barnacles often hide during this vulnerable time.

Land arthropods like centipedes, millipedes, and spiders also have exoskeletons. Features like setae, maxillae, swimmerets, and jointed legs make them adaptable. Their exoskeleton includes compound eyes and sensory organs like antennae and setae, which help them sense their surroundings.

Moulting

Moulting in arthropods happens when they grow and need to shed their old exoskeleton. This exoskeleton is made of chitin and sometimes calcium carbonate. The moulting process involves shedding the old cuticle to reveal a new, larger one.

Arthropods include insects, crabs, spiders, and other species in the phylum Arthropoda. They prepare for moulting by increasing their haemolymph pressure. This pressure helps split the old exoskeleton at specific seams. Next, enzymes are released to separate the old cuticle from the epidermis.

During moulting, arthropods face several challenges:

1. They are vulnerable to predators and environmental hazards since the new exoskeleton is still soft.
2. They risk drying out and getting physically damaged.

Insects and crustaceans like crabs and shrimp must hide until their new exoskeleton hardens. Arthropods have jointed legs and segmented bodies (head, thorax, and abdomen) and use moulting to grow.

Subphyla like Crustacea and Chelicerata include crabs, shrimp, barnacles, and mites. They are all part of the moulting cycle. Marine arthropods like lobsters use swimmerets for movement. Terrestrial ones, like centipedes and millipedes, use legs adapted to land. Sensory setae and compound eyes help them survive during the vulnerable moulting phase.

Internal Organs

The internal organs of arthropods have many functions. They help with breathing, digesting food, and pumping blood. Arthropods have a heart that pumps a fluid called haemolymph through their bodies. Their respiratory systems can vary.

• Insects breathe through tracheal tubes.
• Crustaceans, like crabs and shrimp, use gills.

Internally, the segments of their bodies contain these organs:

• The head has the brain and sensory organs like compound eyes and antennae.
• The thorax has muscles that control the legs, swimmerets, and wings.
• The abdomen holds reproductive organs and parts of the digestive system.

Different groups of arthropods have unique features.

• Insects have a heart that moves haemolymph from the abdomen to the thorax and head.
• Crustaceans like crayfish and lobsters have a more centralized heart.
• Spiders and other similar arthropods have book lungs or gills.
• Land arthropods like millipedes and centipedes have spiracles for breathing.

Their mouthparts, like mandibles and maxillae, show diversity in feeding habits. Barnacles, unlike most arthropods, do not move and use specialized appendages to filter-feed. They grow by molting, shedding their hard exoskeletons, which may include calcium carbonate for added strength.

Respiration and Circulation

Arthropods belong to the phylum Arthropoda. They have various respiratory systems across different groups.

• Insects breathe through tracheal tubes connected to openings called spiracles on their thorax and abdomen.
• Crustaceans, such as crabs and shrimp, use gills to extract oxygen from water. These gills often have setae to increase their surface area.
• Spiders, which are chelicerates, breathe using book lungs or tracheae.

Arthropods have an open circulatory system. In this system, haemolymph is pumped by a heart through vessels into body cavities. This helps in transporting nutrients and waste efficiently.

Their exoskeletons are made of chitin and sometimes calcium carbonate, providing structural support. Marine species like lobsters and crayfish have swimmerets to improve movement and respiration.

Terrestrial arthropods, such as centipedes and millipedes, have spiracles adapted for land environments. Arthropods also molt to grow, shedding their old exoskeletons to reveal new ones.

They have jointed appendages and segmented bodies with a head, thorax, and abdomen. Many also have antennae or mandibles, helping them survive in various habitats.

Nervous System

Arthropods include insects, spiders, crabs, and lobsters. They have a unique nervous system. This system is ladder-like with a chain of ganglia running through their segmented bodies.

Each segment often has its own ganglion. This helps coordinate their movements and behaviors. The cuticle protects these internal structures and often sheds through molting.

The head has sensory organs like compound eyes and antennae. These help arthropods navigate their environment. The thorax and abdomen have additional ganglia. These ganglia regulate advanced movements, like swimming with swimmerets in crustaceans or walking with jointed legs in centipedes and millipedes.

Setae on the exoskeleton act as touch sensors. Bristles detect chemicals. Arthropods, from shrimp and crabs to mites and horseshoe crabs, have complex nervous systems that set them apart from other invertebrates. Unlike simple nerve nets in some marine animals, their ganglia are highly organized.

They also have blood-like haemolymph and calcium carbonate in their exoskeletons. Specialized structures like mandibles, maxillae, and swimmerets help with their versatile behaviors. The subphylum Crustacea includes crayfish and barnacles, showing varied adaptations and development managed by their advanced nervous systems.

Excretory System

Arthropods get rid of waste in different ways. This depends on where they live.

Here are the main organs they use:

1.–Malpighian Tubules–:

• Found in insects and some arachnids like spiders and mites.
• Remove nitrogenous wastes.
• Work with the gut to excrete wastes.

2.–Green Glands–:

• Found in crustaceans like crabs, shrimp, lobsters, and crayfish.
• Located at the base of the antennae.
• Filter waste from the haemolymph before it’s excreted.

These systems differ from the kidneys used by other animals. Malpighian tubules extend into the thorax and abdomen. They absorb wastes from the haemolymph.

Some arthropods use coxal glands near their leg joints for excretion. In chelicerates like horseshoe crabs, these glands process wastes before reaching the hindgut.

Marine species, including some mollusks and barnacles, use specialized excretory organs. Centipedes and millipedes have adapted systems for effective waste removal on land.

All these creatures have an exoskeleton made of chitin. Their internal structures help them survive in various environments, from the sea to land.

Senses in Arthropods

Optical Senses

Arthropods have unique eyes compared to vertebrates. They have compound eyes made up of tiny units called ommatidia. They also have simple eyes like pigment-pit ocelli.

Insects, a group within phylum Arthropoda, often have these eyes on their heads. Crabs, which are crustaceans, and spiders, which are chelicerates, use their compound eyes to detect movement and navigate. These eyes give them a wide field of view. This helps them avoid predators and find food.

Some arthropods, such as shrimp and lobsters, have highly developed compound eyes. These eyes help them in their marine habitats.

Optical senses are important for behaviors like hunting and mating. Barnacles and horseshoe crabs use their simple eyes to sense changes in light. Compound eyes help centipedes and millipedes detect prey. Crustaceans rely on their vision for communication.

The accuracy of these eyes allows arthropods to interact with their environment well. Certain mites and spiders have specialized eyes that improve their hunting skills. These visual systems help arthropods survive and thrive in both land and water environments.

Olfaction

Arthropods include insects, spiders, crabs, and lobsters. They rely on smell to navigate their world.

Insects and crustaceans, like shrimp and crabs, use antennae as their main smelling organs. Spiders and mites use setae.

Antennae, covered with a thin cuticle, detect chemical signals. Insects use them to find food, mates, and avoid danger.

Crayfish and other crustaceans use antennules to sense food in water. Arthropod sense of smell is specialized due to their jointed appendages and segmented bodies.

Spiders and horseshoe crabs use setae to detect chemical cues. Insects have special olfactory receptors on their antennae, maxillae, and mandibles.

Their exoskeleton, made of chitin, protects these structures during molting. The thorax and abdomen hold important sensory equipment, like compound eyes.

Their segmented limbs, including swimmerets in marine crustaceans, help them interact with their surroundings. The diverse subphyla, from scorpions to centipedes and millipedes, show many olfactory adaptations.

Other invertebrates and vertebrates also have systems for smell, but arthropods’ reliance on their antennae and setae makes them uniquely effective.

Reproduction and Development

Arthropods are invertebrates in the phylum Arthropoda. They have different ways of reproducing.

Insects and crustaceans, like crabs, shrimp, and lobsters, usually reproduce through internal fertilization. They produce eggs that turn into embryos. The eggs go through moulting, shedding the old cuticle for a new exoskeleton. This also happens in spiders and chelicerates, such as mites and horseshoe crabs.

Arthropod larvae, like those of crayfish and barnacles, develop through distinct stages until they become adults. Environmental factors, such as temperature and humidity, affect these stages. This influences the survival and growth of land and sea arthropods. For crustaceans, calcium carbonate in the water hardens their new exoskeletons.

Arthropods use their jointed appendages for various activities, such as feeding and moving. Insects use antennae and maxillae. Crustaceans use mandibles, swimmerets, and setae. Developmental processes are similar across many species, whether on land or in water. This shows how adaptable arthropods are to different environments.

Evolution and Evolutionary History

Arthropods appeared over 500 million years ago. Fossils show early forms with jointed legs, body segments, and exoskeletons made of chitin. Trilobites, found in ancient seas, are important fossils of these early arthropods.

Over time, arthropods split into groups like Chelicerata and Crustacea. Modern members include spiders, crabs, and insects. Jointed limbs, diverse sensory tools like compound eyes, and the ability to shed their skin helped them thrive in water, on land, and in the air.

Crustaceans like shrimp and crabs developed special limbs like swimmerets. Insects evolved complex mouthparts like mandibles and maxillae. Their blood, called haemolymph, circulates nutrients and helps their development. Calcium carbonate strengthens the exoskeletons of horseshoe crabs and crayfish.

Barnacles and lobsters show how adapting to different places led to varied body shapes and functions. Antennae help with sensing, while swimmerets aid in movement.

Diversity within Arthropods

Arthropods are very diverse. They live in many habitats and adapt well. Their cuticle, made of chitin and calcium carbonate, helps them survive in different places.

Arthropods have segmented bodies: head, thorax, and abdomen. This helps them specialize. They have jointed appendages like legs, antennae, and swimmerets for movement and various tasks.

Insects are a major group. They have compound eyes and wings. These features help with pollination and finding food.

Crustaceans include crabs, shrimp, and barnacles. They have exoskeletons for protection and support. Some, like lobsters and crayfish, have swimmerets and mandibles.

Spiders and mites, known as chelicerates, have jointed legs and sensory setae.

Centipedes and millipedes, which live on land, have special features for their habitats.

Arthropods grow by moulting, which is shedding their old exoskeleton.

Their haemolymph and maxillae show advanced body functions.

Each subphylum, including crustacea and horseshoe crabs, impacts their ecosystems. They help with pest control and can spread diseases.

FAQ

What are arthropods and why are they called ‘leggy wonders’?

Arthropods are invertebrate animals like insects, spiders, and crustaceans. They are called “leggy wonders” because they typically have multiple pairs of jointed legs, which help them move efficiently and adapt to diverse environments.

How do arthropods use their legs for different purposes?

Arthropods use their legs for walking, jumping, swimming, digging, capturing prey, and grooming. For example, spiders use their legs to spin webs, while grasshoppers use their strong hind legs for jumping.

What are some examples of arthropods with unique leg adaptations?

Some examples of arthropods with unique leg adaptations include mantis shrimp with powerful raptorial appendages, water striders with hydrophobic legs enabling them to walk on water, and tarantulas with specialized scopulae for climbing walls and ceilings.

How do arthropods benefit from having multiple legs?

Having multiple legs allows arthropods to move quickly, effectively hunt for food, and escape predators. They can also carry heavy loads, climb rough surfaces, and efficiently burrow into the ground or navigate through water.

What role do arthropod legs play in their survival and reproduction?

Arthropod legs play a crucial role in their survival and reproduction by allowing them to move, hunt, defend themselves, and engage in mating behaviors. For example, a spider’s legs help it capture prey and build webs, while a male praying mantis uses its legs to grasp and hold onto a female during mating.