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Transcript of Arthropods
Karthik Elyes The most common arthropods include insects, crustaceans, and arachnids.
They make up more than 80% of living species on earth and are one of the two animal groups that successfully live on dry environments.
Crabs Lice Shrimp Spiders Scorpions Centipedes Millipedes. Characteristics They are characterized by jointed limbs and cuticles which are mainly made of chitin.
One of the most recognized characteristic is the periodical molting because the cuticles inhibits growth.
The cuticles of crustaceans are biomineralized with calcium carbonate.
An arthropod body consists of repeated segments, each with a pair of appendages.
Morphology The arthropods main internal cavity is called the hemocoel, it accommodates the internal organs.
Their internal organs are also made up of repeated segments. Their nervous systems are “ladder like” with ventral nerve cords that form the ganglia in each segment. The excretory and respiratory systems vary differently between the different subphylum.
Most of the species, the ocelli can only detect the direction of light. While the compound eyes are the main source of information. In arachnids, the ocelli can actually create and image and the compound eyes can swivel to track prey.
The methods of reproduction vary from species. Terrestrial species use internal fertilization.Aquatic species use either internal or external fertilization. Except for scorpions all arthropods lay eggs.Scorpions give birth to live young after the eggs have hatched inside the mother. Arthropods have open circulatory systems.
The heads are formed by the fusion of various segments. The ganglia at the end of the nerve cords form the brain that encircles the esophagus.
The vision relies on compound eyes and pigment-pit ocelli.
They have chemical and mechanical sensors that are modifications of the many setae that project through the bristles.
Embryology Arthropods are protostomes, this means that while they are embryos, the blastopore forms the mouth downward to the anus. Also, Arthropods are triploblastic, this means that they have three germ layers ( Mesoderm, Endoderm, Exoderm) An arthropods body cavity is a hemocoel, which allows room for the creature's organs and for the creature's blood to pass through its body. Arthropods produce large, yolk filled eggs encased in a protein shell. The embryo develops excretory organs that are located on its head, leg or sometimes abdomen. They also develop compound eyes and a serotonergic nervous system. Arthropods have an exoskeleton made of chitin. Most arthropods do not have blood vessels but instead an open circulatory system. Arthropods have either single or double jointed appendages. Their exoskeleton protects from water loss, and allows their muscles a structure to pull on. An arthropods nervous system connects to the outside of its exoskeleton allowing for senses similar to our sense of smell, touch, and taste
Life History of Arthropods Arthropods first appeared in the sea.
Arthropods do not have an ancestor that is an arthropod, however shared a common ancestor. Isopods, also known as "pillbugs" or "roly-pollies" were the first crustaceans to invade the land. Life History of Spiders Spider fossils are rare because spiders' bodies are very soft. The oldest known amber that contains fossil arthropods dates from 130 million years ago in the Early Cretaceous period. The oldest known amber that contains fossil arthropods dates from 130 million years ago in the Early Cretaceous period. The spider is one of the oldest arthropods with one of the most diverse species of its sub phylum. The amount of variable traits are staggering. The spider remains to this day one of the most populace arthropods in the world. The most interesting methods capturing of prey using a web. With literally thousands of different types of webs and techniques used to capture prey Biochemical Evidence Chitin, a polymer of GlcNAc or N-Acetylglucosamine, is the second most abundant biopolymer on Earth (cellulose is the most abundant).
Chitin is a major component of the rigid, cuticular exoskeleton of all Arthropod, they spend considerable resources for this structure.
Chitin is a polysaccharide that is a derivative of glucose. It is synthesized from groups of N-Acetylglucosamine. They form linkages similar to those of glucose in cellulose.
Chitin is basically described as a cellulose with one hydroxyl group on each monomer substituted with a acetyl amine group. This setup allows for increased hydrogen bonds between adjacent polymers giving the chitin-polymer matrix increased strength.
Recently, genetic screens have demonstrated that mutations in genes necessary for chitin polymerization, modification, and disassembly independently affect tracheal diameter or length of the Drosophilia. All arthropods have bilateral symmetry. They all have a relatively hard exoskeleton. One that defends them from others. Cuticle Crab Molting Segments Spider Internal Cavity Internal Organs of a Spider Open Circulatory System Chitin Wasp Ocelli PillBug Oldest Spider Web Amber Wolf Spider s