Arthropods


 * By: Rachel Yoo**


 * Phylum:** Arthropod
 * Subkingdom:** Eumetazoa
 * Class:** Myriapods (Diplopods and Chilopods), Trilobites, Chelicerates (Arachnids), Crustaceans, and Insects


 * Body Plan:** Arthropods have five branches, or classes, that all derive from the same ancestor. Yet, Arthropod phylum all share certain characteristics. To begin, the Arthopods have a segmented body plan, which is also called metamerization. Even though the body is segmented into the head, thorax and abdomen, there is no separation internally. These segmented body parts are protected by the exoskeleton made primarily of chitin and then hardened with sclerotin or with calcium carbonate. Within the body, the arthropods circulate through an open circulatory system with a hemocoel and have a dorsal brain and a ventral nerve cord. Finally, Arthropods have jointed appendages, which are modified for different functions such as the antennae, jaws, legs, etc.




 * Germ Layers:** Arthropods are triploblastic, or having three germ layers know as endoderm, mesoderm and ectoderm.
 * Symmetry:** All Arthropods have a bilateral symmetry.
 * Coelomate:** Arhtropods are coelomates for they have the true coelom, which is completely enclosed within the mesoderm layer.


 * Habitat:** Confining the entire group of Arthropods into one specific habitat is impossible because it is the largest living animal species. They have a fairly diverse array of habitats ranging from aquatic environments to terrestrial environments. Despite its large size, the Arthropods have seven general habitats: Florida scrub, flatwoods, bayheads, seasonal ponds and seeps, Lake Annie, pastures, and disturbed habitats (habitats that have been contacted by humans). Yet, Arthropods still cannot be confined to these locations because they are EVERYWHERE.
 * Movement:** In Greek, //Arthropoda// means "jointed foot". These jointed appendages along with the muscles attached within the skeleton allows movement to be possible.
 * Skeletal System:** Unlike humans, Arthropods have their skeletal system on the outside called exoskeleton.


 * Evolutionary Advancement:** First introduced to the Earth during the Cambrian period, Arthropods were more advanced than their ancestors, which are believed to be worm-like animals. Having the exoskeleton and the jointed limbs, they are believed and proven to be the most successful animal Phylum through its large numbers and species. Their exoskeleton shell does provide the information that during the Cambrian period, defense was crucial and Arthropods took on the caution to protect themselves from competitors. Finally, they were the first taxon of species to possess the more advanced receptors like photoreceptors (eyes) and chemoreceptors.


 * Feeding Patterns:** Because of the array of arthropods, they all obtain food through different means. Arthropods can be carnivores, herbivores, detritus feeders, filter-feeders, and even parasites. Therefore, they obtain food differently through their adaptations such as filter-feeding, mouth parts for sucking fluids, or even mouth parts for chewing and cutting.




 * Respiration:** Arthropods all respire differently as well: gills, trachea, and book lungs. Crustaceans use gills, which exchanges gas when in contact with water. Trachea is used by terrestrial arthropods, and they have tubes within their body that come in contact with the surface of the body and the environment for air. Finally, the book lung is a respiratory organ, which comes into contact with the outside air through the small slit in the exoskeleton to exchange oxygen and carbon dioxide.




 * Circulation:** Arthropods have an open circulatory system with a hemocoel, which is a cavity between the organs where the blood is circulated.


 * Excretory:** Arthropods either have paired excretory organs (maxillary, antennal, or coxal glands) or Malpighian tubules. The paired excretory organs open at the base of particular appendages while the Malpighian tubules open into the intestines, but overall, both organs allow the waste to exit through the anus. In addition, Arthropods have the ability to conserve water by producing a urine that is much more concentrated in salt compared to their blood allowing them to excrete less water.


 * Nervous:** Consisting of the dorsal brain and the ventral nerve cord, Arthropods have a nervous system different from vertebrates. Instead of having one neuron supplying multiple muscles cells, arthropods' small muscles prevents this organization and need multiple neurons to work with one muscle cell to allow movement.


 * Reproduction:** Most often than not, Arthropods are separated into males and females, and their sex organs are located down in the abdomen. Sperm is commonly transferred through the use of spermatophores, which are sealed packets of sperm. This method helps to protect the sperm from being diluted in the water or desiccated on the land. The spermatophores can be directly transferred into the female or some deposit them into the ground. Although this method is common, some arthropods ,such as crustaceans, millipedes, some insects, spiders, and some mites, transfer free sperm.

[|http://userwww.sfsu.edu/~biol240/labs/lab_19arthropod/pages/arthrochars.html] [] [] [] [] [] [] [] []
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http://www.britannica.com/EBchecked/topic/36943/arthropod/42368/Excretory-system-and-water-balance