Arthropods Study Guide

Introduction

The phylum Arthropoda has about nine million species. All the arthropods, whether they are aquatic, terrestrial, or parasitic, have a chitinous exoskeleton and appendages that are jointed. This phylum is one of the most diverse animal groupings on the planet, including multiple large classes, like the largest phylum of the animal kingdom. Aquatic arthropods can survive in any environment.

What are arthropods?

Have you ever encountered an arthropod? You’ve almost certainly never seen an ant up close. Is that a moth you’re observing?

For every one of the more than a million arthropod species known (and many more still to be found), there are possibly a million more that you have never heard of. Arthropods come in a wide variety of species, and in truth, the animal world has about 5 million distinct species.

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Arthropoda characteristics

The features of arthropods are:

• Segmented triploblastic entities with bilateral symmetry.
• They are constructed in a manner that resembles the complexity of an organ system.
• The body is divided into three parts: the head, the thorax, and the belly.
• Their appendages are joined, enabling them to move more freely and fast.
• Red blood cells fill the coelomic chamber.
• They are capable of having an open circulatory system.
• A pair of compound eyeballs embellish the head.
• Chitin is used to construct the exoskeleton.
• According to the species, malpighian tubules excrete water-borne arthropods, while green or coaxal glands excrete land-based arthropods.
• They have single-sex and may be fertilized externally or internally.
• They possess an advanced digestive system.
• They breathe via the trachea, positioned on their bodies’ surface.
• They have hair, antennae, simple and sophisticated eyes, hearing organs, and statocysts.

Arthropod species

There are four surviving subphyla within the phylum Arthropoda, which translates as “jointed feet”:

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• Chelicerata is a class of animals that includes spiders, mites, and scorpions. The first pair of appendages of these organisms are used to grab food where a pair of teeth or pincers may be observed. Spiders with eight legs are an example.
• Centipedes and millipedes are both classified as Myriapoda. Appendages vary from ten to nearly 200 pairs in these land-dwelling species.
• Insects are classified as members of the genus Hexapoda. These animals have taken over the earth, and each hexapod has three pairs of walking limbs.
• Crustaceans include crayfish, shrimp, lobsters and crabs. These animals have mandibles, modified appendages used for grabbing, biting, and chewing food.

Classifications of the phylum Arthropoda

The phylum Arthropoda is classified as follows:

Crustacea

• They may be found on land, water, or as parasites.
• The cephalothorax is the thorax section that connects the head to the body.
• Respiration occurs through the gills or the whole surface of the body.
• A single massive carapace encases the whole body.
• Each of them has two pairs of antennae and five pairs of appendages.
• They eliminate waste using these glands.
• They have gonopores and an intricate set of eyes.
• The road to advancement is long and twisted, and a larval stage is included in the mix.
• Two examples are Daphnia and Palaemon.

The Crustacea subphylum is divided into six groups:

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

Myriapoda

• These are found mostly on the ground.
• The body is long and stretched because of its several pieces.
• The head is equipped with antennae, two jaws, and a pair of rudimentary eyes.
• They have an abundance of legs.
• Upper and lower lips include epistome and labrum, respectively; the lower lip contains maxillae.
• The mouth has two mandibles.
• They breathe via the trachea and discharge waste through the Malpighian tubules.
• Two examples are Julus and Scolopendra.

The subphylum Myriapoda is divided as follows:

• Chilopoda
• Diplopoda
• Pauropoda
• Symphyla

Hexapoda

• They are most often seen on the ground.
• The human body may be divided into the head, thorax, and belly.
• On the skull, the pre-segmental Acron is visible.
• The thorax is composed of three sections.
• The abdomen is divided into seven to eleven sections.
• They are equipped with three sets of limbs and legs.
• On its face, compound eyes are visible.
• Their gills and trachea enable them to inhale and exhale.
• The Malpighian tubule is used for excretion.
• There is a larval stage, and development is gradual.
• Mosquitoes, ants are just a few species that fall under this category.

The phylum Hexapoda is divided into two suborders:

• Insecta
• Entognatha

Chelicerata

• They are often found on land.
• The human body is divided into two different parts: the cephalothorax and the abdomen.
• Antennas are not present.
• A distinct number identifies each part of the abdomen.
• On the interior, it contains four pairs of appendages.
• Depending on the species, they breathe via their trachea or gills.
• The Malpighian tubules play a critical role in excretion.
• For example, an area with Limulus.

The Chelicerata subphylum is classified into the following classes:

• Arachnida
• Merostomata
• Pycnogonida

Onychophora

• These are small terrestrial arthropods.
• Human body segments may be discovered.
• The nephridia are the organs in charge of waste elimination in the body.
• The trachea is used to inhale and exhale.
• For instance, Peripatus.

Trilobitomorpha

• These are primordial, extinct arthropods.
• They were abundant throughout the Paleozoic era.
• The body was divided into a central lobe and two on either side.
• The creature’s head was equipped with intricate eyes and two antennae.
• There was no visible distinction between the different bodily sections.
• The creature’s head, thorax, and pygidium were dissected.
• Appendages are classified into two types: limbs and digits.

There is just one class in the subphylum, which is Trilobita.

Conclusion:

• Arthropods are classified into four distinct living subphyla: chelicerates (which includes spiders, mites, and scorpions); myriapods (which includes centipedes and millipedes); hexapods (which includes insects); and crustaceans (which include worms and crustaceans).
• Arthropods have a segmented body, a tough exoskeleton, and appendages that function as feeding devices, sensory structures, defense mechanisms, and locomotion systems.

FAQs:

1. Give five examples of arthropods.

Some examples of arthropods are – Lobsters, Crabs, Spiders, Centipedes, And Millipedes.

2. What are the five characteristics of arthropods?

• Exoskeleton
• Bodies with segments
• Appendages are joined
• Symmetry on all sides
• The circulatory system is open

3. What are the 3 main body parts that all arthropods have?

Head, thorax, and abdomen.

4. What are the main features of arthropods?

• They have an exoskeleton.
• They have appendages that are joined.
• Their body is divided into sections.
• They are uniform on both sides.
• They have a circulatory system that is permeable.

5. What are the main morphological features of arthropods?

Three characteristics distinguish arthropods:

• They are metameric creatures (segmented bodies)
• They have a chitin exoskeleton
• They have articulated limbs

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Sources:

1. Morphology. http://www.biology.ualberta.ca/parasites/ParPub/text/text/arthr01b.htm. Accessed 7 Dec, 2021.
2. Arthropods. https://www.ck12.org/biology/arthropods/lesson/Arthropods-MS-LS/?referrer=concept_details/. Accessed 7 Dec, 2021.
3. Arthropods. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/11.10/primary/lesson/arthropods-bio/. Accessed 7 Dec, 2021.

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