An arthropod is an invertebrate animal phylum Arthropoda, and include the insects, arachnids, crustaceans, and others. Arthropods are characterized by their jointed limbs and cuticles.
The skeletal system in the phylum, arthropoda, is made up of invertebrate and insects with exoskeletons. An exoskeleton means that the skeleton is outside of the insect.
Arachnids
An arachnid's skeletal system is mainly their outermost layer, the exoskeleton. They are
joint-legged invertebrate animals. All arachnids have eight legs. Arachnids also have two further pairs of appendages that have become adapted for feeding, defense, and sensory perception. They have no antennae or wings. Their body is organized into two tagmata called the prosoma, and the opisthosoma. They also have an internal structure of cartilage-like tissue called the endosternite, to which certain muscle groups are attached.
joint-legged invertebrate animals. All arachnids have eight legs. Arachnids also have two further pairs of appendages that have become adapted for feeding, defense, and sensory perception. They have no antennae or wings. Their body is organized into two tagmata called the prosoma, and the opisthosoma. They also have an internal structure of cartilage-like tissue called the endosternite, to which certain muscle groups are attached.
Crustaceans
As explained before, crustaceans' skeletal systems are on the outside of the body and are known as exoskeletons. The exoskeletons of crabs and lobsters are made of chitin, which is responsible for making the shells hard. The shells of crustaceans provide more than just a shield of protection for these two groups of marine life. The shells also provide a large variety of life sustaining functions for these small sea creatures as their exoskeleton. Crustaceans go through a molting process as they grow. A new exoskeleton grows underneath the existing one the process takes two to four days. Once the new exoskeleton is in place, the old one is shredded. It takes an additional two to three days for the new one to completely attach and adjust to the crustacean's body. The shell also provides support for the muscles and joints so it can move about freely.
The insect outer skeleton, the cuticle, is made up of two layers: the epicuticle, which is a thin and waxy water resistant outer layer and contains no chitin, and a lower layer called the procuticle. The procuticle is chitinous and much thicker than the epicuticle and has two layers: an outer layer known as the exocuticle and an inner layer known as the endocuticle. The tough and flexible endocuticle is built from numerous layers of fibrous chitin and proteins, criss-crossing each others in a sandwich pattern, while the exocuticle is rigid and hardened. The exocuticle is greatly reduced in many soft-bodied insects, especially during their larval stages.
Insects are the only invertebrates to have developed active flight capability. Their muscles are able to contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible. Having their muscles attached to their exoskeletons is more efficient and allows more muscle connections. Crustaceans also use the same method, but spiders use hydraulic pressure to extend their legs. Unlike insects, though, most aquatic crustaceans are biomineralized with calcium carbonate extracted from the water.