CURRICULUM SUPERFRIENDS: invertebrate animal phylum Arthropoda

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.

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.

Skeletal System

Art:Representative arthropods. Uniramia, the largest of the arthropod subphyla, contains mostly terrestrial insects and myriapods (including centipedes and millipedes). The insects, the largest arthropod class, differ from other arthropods in that they are usually winged and have only three pairs of legs. Members of the Crustacea subphylum are mostly marine-dwelling and include the shrimps, lobsters, crabs, and barnacles. The microscopic water fleas are chiefly found in fresh water and, along with other minute members of this subphylum, are part of the zooplankton. Most members of the Chelicerata subphylum are arachnids, including the spiders, scorpions, ticks, and mites. The trilobites (members of the Trilobita subphylum) are extinct marine arthropods that flourished during the Cambrian Period. Fossilized remains show a body having three longitudinal lobes divided into three regions—head, thorax, and tail.

Representative arthropods. Uniramia, the largest of the arthropod subphyla, contains mostly terrestrial insects and myriapods (including centipedes and millipedes). The insects, the largest arthropod class, differ from other arthropods in that they are usually winged and have only three pairs of legs. Members of the Crustacea subphylum are mostly marine-dwelling and include the shrimps, lobsters, crabs, and barnacles. The microscopic water fleas are chiefly found in fresh water and, along with other minute members of this subphylum, are part of the zooplankton. Most members of the Chelicerata subphylum are arachnids, including the spiders, scorpions, ticks, and mites. The trilobites (members of the Trilobita subphylum) are extinct marine arthropods that flourished during the Cambrian Period. Fossilized remains show a body having three longitudinal lobes divided into three regions—head, thorax, and tail.

Phylum Arthropoda: The Arthropods

Most successful animal group ever to live
Consists of over 1 million named species, 2 of every 3 animals are arthropods. ~ 10¹⁸ individuals.
Inhabit all ecosystems

General characteristics