Logan Steele
Arthropods are invertebrates with segmented bodies and jointed limbs. They are the largest phylum of invertebrate animals and include crustaceans, insects, arachnids, and other classes. Arthropods have a hard, protective exoskeleton (external skeleton) made of chitin, a polymer of N-Acetylglucosamine, which provides a large surface area for the attachment of muscles. This exoskeleton, along with the muscles, supports movement and protects the organism. The muscles of arthropods are primarily striated, similar to the skeletal muscles of humans, and they are designed to exert force against the exoskeleton to enable movement.
| Characteristics | Values |
|---|---|
| Arthropods | Invertebrates with segmented bodies and jointed limbs |
| Arthropod muscles | Primarily striated (similar to skeletal muscles of humans) |
| Arthropod skeleton | External (an exoskeleton) |
| Muscle movement | Muscles are attached to the inner surface of the exoskeleton |
| Muscle contraction | The contraction rate of striated muscles is faster than smooth muscles |
| Muscle function | Muscles exert force against a rigid skeleton |
| Muscle types in crustaceans | Aerobic and anaerobic |
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What You'll Learn
- Arthropods have exoskeletons, which are external skeletons
- Arthropods have segmented bodies and jointed limbs
- Arthropod muscles are primarily striated, like human skeletal muscles
- Arthropods have a wide variety of respiratory systems
- Arthropods have a reduced coelom, a membrane-lined cavity between the gut and body wall
Arthropods have exoskeletons, which are external skeletons
Arthropods are a phylum of invertebrate animals that includes crustaceans, insects, arachnids, and other classes. They are distinct from vertebrates in that they possess an exoskeleton, a skeleton that is on the exterior of the body, rather than an internal endoskeleton. This exoskeleton is a hard, protective covering that supports the body's shape and protects the internal organs. It is composed of a thin, outer protein layer, the epicuticle, and a thick, inner chitin-protein layer, the procuticle. The exoskeleton provides a large surface area for the attachment of muscles and enables arthropods to move in a variety of ways, including walking, running, swimming, and flying.
The evolution of the exoskeleton in arthropods required solving two functional problems: how to allow for growth and how to enable movement. The problem of growth is solved through molting or ecdysis, the periodic shedding of the old exoskeleton. The underlying cells release enzymes that digest the base of the old exoskeleton and then secrete a new one beneath it. The old skeleton is then split along specific lines, and the arthropod pulls out of it. The new exoskeleton is soft and flexible, and it is stretched by localized, elevated blood pressure and the intake of water or air.
The exoskeleton provides support and protection for arthropods, but it also imposes limits on their maximum size, especially for land-dwelling species. The largest arthropods are found in the sea, where they benefit from the buoyancy of seawater. On land, a larger bulk would require an excessive amount of skeleton for support, and the new soft skeleton after molting may collapse. This is one reason why gigantism is rare in arthropods compared to vertebrates.
The exoskeleton of arthropods is divided into different functional units called tagmata, which are adapted to different functions in the body. For example, the tagmata of insects include the head, thorax, and abdomen. Each segment has sclerites, or areas of rigidity, according to its requirements. In some beetles, the joints are so tightly connected that the body is practically in a rigid box, while in other arthropods, the tagmata are connected by flexible cuticle and muscles, allowing for freedom of movement.
The limbs of arthropods are jointed, and the internal surface of the exoskeleton often has infoldings called apodemes that serve as attachment sites for muscles. These structures are composed of chitin and are stronger and stiffer than vertebrate tendons. They can also store elastic energy for jumping, as seen in locusts. The exoskeleton is periodically shed through molting, which is necessary for the growth of arthropods. During this vulnerable period, the arthropod gulps air or water to hold its form until the new skeleton hardens.
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Arthropods have segmented bodies and jointed limbs
Arthropods are invertebrates in the phylum Arthropoda. They are characterised by a hard, protective exoskeleton (external skeleton) with a cuticle made of chitin, often mineralised with calcium carbonate. This exoskeleton covers virtually all external structures, as well as a few internal ones, including eyes, mouthparts, antennae, and more. The exoskeleton is divided into separate plates to assist in movement, with joints between body segments and limb sections covered by flexible cuticle.
Arthropods have segmented bodies, with each body segment encased in hardened cuticle. This segmentation is a defining feature of the group, with the body typically divided into a head, an abdomen, and a thorax. The segments have a varied number of segments with attached, paired, jointed appendages. The appendages are adapted for various types of locomotion, including walking, running, swimming, and burrowing. The posterior pairs of appendages often function as swimming legs, the middle pairs as walking legs, and the anterior pairs as food-getting apparatuses or sensory organs.
The largest arthropods are aquatic, as they gain considerable support from the buoyancy of seawater. On land, an excessive amount of skeleton would be required to support a large bulk, and the new soft skeleton after moulting might collapse. Moulting is a necessary process for arthropods to grow, but it leaves them essentially soft-bodied and vulnerable until the new skeleton hardens. Arthropods cannot rely on their muscles to define their form in the same way that soft-bodied animals do, as their muscles are designed to exert force against a rigid skeleton.
Arthropods have long, jointed limbs, which, along with other jointed appendages, account for the great freedom of movement enjoyed by terrestrial arthropods and vertebrates. The combination of an exoskeleton and jointed appendages is analogous to a suit of armour. The exoskeleton provides a large surface area for the attachment of muscles, and it functions in support, movement, and protection from the external environment. Its cylindrical design resists bending and provides structural support, allowing arthropods to retain their characteristic physical form and resist the stresses of locomotion.
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Arthropod muscles are primarily striated, like human skeletal muscles
Arthropods are invertebrates with segmented bodies and jointed limbs. They are the largest phylum of invertebrate animals and include crustaceans, insects, arachnids (spiders and scorpions), and other classes. Arthropods have a hard, protective exoskeleton (external skeleton), which is the opposite of vertebrates, who have an internal skeleton called an endoskeleton. The exoskeleton provides a large surface area for the attachment of muscles and, in addition to functioning in support and movement, also provides protection from the external environment.
The muscles of arthropods are primarily striated, like the skeletal muscles of humans. Striated muscle has a much faster contraction rate than smooth muscle, and this feature probably enabled the development of flight in many insects. All arthropod muscles seem to be striated, and the sarcomeres are of varying lengths. In locusts, the sarcomeres of wing muscles are 3.9 micrometres (μm) long, while the sarcomeres of leg muscles are 8.5 μm long. The principal wing muscles are the dorsoventral muscles, which run vertically from the sternum to the tergum, and the longitudinal muscles, which run lengthwise along the segment.
The exoskeleton of arthropods and the attachment of muscles to it play a crucial role in their movement and form. The exoskeleton, with its cylindrical design, resists bending and provides structural support. The muscles attached to the inside of the exoskeleton enable arthropods to move in various ways, such as walking, running, swimming, and flying. Arthropods are unique among invertebrates as they lack locomotory cilia, even in the larval stage. Instead, they rely on their exoskeleton and muscles for movement.
It is worth noting that arthropods with soft bodies, such as those in the early stages of life, may not fully depend on their exoskeleton for movement. In such cases, the principle of the hydrostatic skeleton comes into play, where muscles compress a membrane-lined cavity (coelom) to change the animal's shape and enable movement. However, as arthropods mature, their muscles become designed to exert force against a rigid skeleton, and their movement becomes more dependent on the exoskeleton.
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Arthropods have a wide variety of respiratory systems
Terrestrial arthropods, on the other hand, possess tracheae and book lungs as respiratory organs. Tracheae are a system of tiny tubes that allow gases to enter the body. In insects, the tracheoles are embedded in the tissues, even within muscle cells. The tracheal tubes are molted along with the exoskeleton. The book-lung system is seen in spiders, where they combine with tracheae for respiration.
The respiratory system of arthropods is separate from their circulatory system. Arthropods possess an open circulatory system with a dorsal heart and a system of arteries. The blood is oxygenated in the gills as it returns to the heart. Insects lack a respiratory pigment as oxygen is delivered directly to the tissues.
Arthropods have an external skeleton (exoskeleton) that provides a large surface area for the attachment of muscles. This exoskeleton is made up of separate plates to assist in movement and provide protection. The cylindrical design resists bending and supports the weight of the organism. The exoskeleton also allows for the great freedom of movement enjoyed by terrestrial arthropods.
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Arthropods have a reduced coelom, a membrane-lined cavity between the gut and body wall
Arthropods are invertebrates that comprise crustaceans, insects, arachnids (spiders and scorpions), and other classes. They are unusual among invertebrates as they lack locomotory cilia, even as larvae. Most arthropods move using their segmental appendages, the exoskeleton, and muscles.
The coelom is the main body cavity in many animals, including arthropods, and is positioned inside the body to surround and contain the digestive tract and other organs. It is derived from the Ancient Greek word κοιλία (koilía) 'cavity'. The coelom is the mesodermally lined cavity between the gut and the outer body wall. During the development of the embryo, the coelom forms in the gastrulation stage. The developing digestive tube of an embryo forms as a blind pouch called the archenteron. In protostomes, the coelom forms by a process known as schizocoely. The archenteron initially forms, and the mesoderm splits into two layers: the first attaches to the body wall or ectoderm, forming the parietal layer, and the second surrounds the endoderm or alimentary canal, forming the visceral layer. The space between the parietal layer and the visceral layer is known as the coelom or body cavity.
In some protostomes, the embryonic blastocoele persists as a body cavity. These protostomes have a fluid-filled main body cavity that is unlined or partially lined with tissue derived from mesoderm. This fluid-filled space surrounding the internal organs serves several functions, such as the distribution of nutrients and removal of waste or supporting the body as a hydrostatic skeleton.
In arthropods, the coelom is reduced and is known as the haemocoel.
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Frequently asked questions
Yes, arthropods have skeletal muscles. They are invertebrates with segmented bodies and jointed limbs. Arthropods have a hard, protective exoskeleton (external skeleton) made of chitin, a polymer of N-Acetylglucosamine. The muscles for movement are attached to the inner surface of the exoskeleton.
Most arthropods move using their segmental appendages, the exoskeleton, and muscles. Their appendages have been adapted for locomotion, including walking, pushing, running, swimming, and burrowing.
Arthropod muscles are primarily striated, like the skeletal muscles of humans. This means they have a much faster contraction rate than smooth muscles, which likely enabled the development of flight in many insects.
Arthropods grow by moulting, or shedding, their exoskeletons periodically. During this process, they form a larger exoskeleton to accommodate their expansion.
