Arthropods

An “arthropod” is an invertebrate animal that has an exoskeleton a segmented body and jointed appendages. The following families of organisms are examples of arthropods:

• Insects such as ants, dragonflies and bees.
• Arachnids such as spiders and scorpions.
• Myriapods (a term meaning “many-footed”) such as centipedes and millipedes
• Crustaceans such as crabs, lobsters and shrimp

It may be useful to remember that the term “arthropod” comes from the Greek words for “arthropod”. foot articulated “. If the organism has an exoskeleton with joints between its feet and body, it is probably an arthropod!

Arthropods are a lineage of life that evolved skeletons on the outside, their hard shells, made of a material called “arthropods”. chitin “instead of inside for structural support.

Arthropod bodies also have other important differences from those of vertebrates like us: their organ systems are simpler and less efficient, which limits the size that arthropods can reach.

An ant the size of a human, for example, would not be able to pump oxygen through its blood to nourish all its tissues, since the circulatory system of arthropods is simpler and less efficient than that of humans.

All arthropods are believed to have evolved from a single common ancestor, although scientists are not sure what this common ancestor looked like or exactly when it lived.

Characteristics of arthropods

Characteristics shared by all arthropods include:

• Exoskeletons made of chitin
• Highly developed sense organs
• Jointed limbs (limbs must be jointed like joints in a suit of armour, as the exoskeleton is rigid and cannot bend to allow movement)
• Segmented bodies
• Nervous system ventral . “Ventral” means “in front”, so this means that the nervous system of arthropods runs along the front of their bodies, near their stomachs, rather than along their backs like the spinal cord of animals.
• Bilateral symmetry . This means that the left and right sides of an arthropod are equal: it will have the same number and arrangement of legs, eyes etc. on the right side of his body than on the left.

Types of arthropods

Trilobites

Trilobites were an ancient family of marine arthropods that went extinct during the extinction event Permian-Triassic . Nowadays, we know them mainly from fossils as shown below.

They lived at the bottom of the ocean and occupied ecological niches similar to those occupied by crustaceans today.

Cheliceratos

The Chelicerata are a branch of the arthropod family tree that, at first glance, may not appear to be related to each other.

This family includes arachnids (such as spiders and scorpions), sea spiders (which resemble arachnids but have some important differences) and horseshoe crabs (which, despite their name, have important differences from other crustaceans).

Myriapods

The term “myriapod” means “many-legged”, so it is not surprising that centipedes, millipedes and other many-legged creatures are part of this family.

Myriapods can have from fewer than ten legs to more than 750. That seems excessive.

Myriapods are typically found in forests and other ecosystems where there is plenty of decaying plant and animal material for them to feed on.

Crustaceans

Crustaceans are a family of mainly aquatic arthropods that includes lobsters, crabs, shrimps, crayfish, barnacles and the odd one out: wood lice, also known as wood lice or “roly polys”.

Unlike their aquatic cousins, wood lice live primarily on land and are found in environments such as gardens and forests, where they survive by eating decaying plant and animal material.

You may also be surprised to see barnacles included in this list: adult barnacles develop hard shells that attach them to their environment, such as the bottom of boats or other underwater surfaces.

But early in their lives, before freezing in place, barnacles have leggy bodies much like other crustaceans.

Hexapods

The term “hexapod” literally means “six feet”. It may not surprise you to learn that insects, which have six legs, are hexapods.

Insects include most “bugs” with six legs, such as flies, ants, termites, beetles, dragonflies, mosquitoes, cockroaches, butterflies and moths.

There are also three much smaller groups of animals in the “hexapod” category. Collembola, Protura and Diplura were once considered insects, but were later found to have small differences that set them apart from other insects.

Examples of arthropods

Ants

When you think of a stereotypical arthropod body, you probably think of an ant. Ants have hard exoskeletons and jointed legs. They also have bodies that are clearly segmented into head thorax and abdomen .

Ants show a type of social organisation that has been developed by arthropods. Ants, bees and termites are what are called “eusocial” organisms: organisms that live in an extreme degree of cooperation, with “colonies” that almost operate as a single organism.

Most arthropod species are not eusocial, but life in eusocial colonies is one of the fascinating paths that arthropod evolution has taken.

Spiders

Spiders are also arthropods, possessing hard exoskeletons, segmented bodies and jointed limbs.

Spiders usually eat smaller arthropods, such as mosquitoes and flies, although they will eat any living thing they can catch, and some particularly large spiders have been known to eat birds or rodents!

Spiders have evolved a variety of strategies to trap their prey: some spin sticky, almost invisible webs in which prey wander and get stuck. Others are active hunters, including jumping spiders that can jump at extreme speeds using special mechanisms in their legs.

Some spiders combine these two strategies, such as “trapdoor” spiders, which set traps by creating hiding places for themselves, then jumping to grab passing unsuspecting prey!

Locusts

With lobster being considered a luxury food nowadays, it is easy to forget that lobsters are in the same family as spiders and ants.

Crustaceans can grow larger underwater than on land, and lobsters can weigh almost 50 pounds!

The body design of lobsters has changed little over the last 100 million years and their anatomy is spectacularly bizarre. The lobster’s kidneys are located in its head, its brain in his throat and his teeth in its stomach . Their “ears” for picking up sound are on their legs and their taste buds, like those of insects, are on their feet.

Butterflies

Butterflies are the most famous example of metamorphosis of arthropods .

At some point in their life cycle, all arthropods undergo a drastic change from their larval stage to their adult form. But butterflies are the only ones whose adult forms are so beautiful that we pay attention to this change.

The common features of the exoskeleton, jointed limbs and segmented body can be seen in adult butterflies.

Facts about arthropods

• Arthropods colonised the land about 100 million years before vertebrates. It is believed that colonising the land was easier for them for several reasons, including the fact that they had already developed legs, which they used to walk on the seabed.
• Approximately 80% of all animal species are arthropods! We don’t see them very often in our daily lives, but all species of insects and crustaceans on Earth add up!
• All arthropods undergo metamorphosis, a process in which their bodies change radically as they move from their larval stage to adulthood. Butterflies are best known for entering cocoons as caterpillars and emerging quite differently, but all arthropods do something similar!
• When arthropods outgrow their old exoskeleton, they have to molt, leaving behind their skin old skin and growing a new one. All arthropods have to do this at least once in their lives.
• Crustaceans and arachnids, two types of arthropods, have blue blood instead of red blood! This is because their blood uses a compound of copper blue to transport oxygen, instead of the compound of iron red used by animals.
• The hard exoskeletons of arthropods are made of chitin, which is made from a derivative of the sugar glucose! But chitin wouldn’t taste sweet and you couldn’t eat it; to make it hard and tough, the glucose is modified so that our bodies no longer recognise it as sugar.
• Common ancestor common ancestor : a common ancestor is an individual or species from which multiple individuals or species evolved.
• Evolution the process by which populations change over time, due to random mutations and the pressures of human activity. natural selection .
• Extinction The process by which a species ceases to exist after the death of its last member. Most species that have lived on Earth to date are now extinct.