Arthropoda


 * Arthropoda**

**Arthropoda:** a phylum of invertebrate animals (as insects, arachnids, and crustaceans) having a segmented body and jointed appendages.
 * Definitions :**

One of the internal respiratory tubes of insects and some other terrestrial arthropods.
 * Tracheae:**

Arthropods are animals that have an exoskeleton and jointed appendages. With **Arthro** meaning joint, and **Poda** meaning foot, all of these animals that fall under this phylum are in segments of jointed exoskeleton. Three fourths of the known living animals and fossils are under this phylum. These animals have conquered land, sea and air. The number of living arthropods are in the tens of millions. This phylum covers many of the insect world. Like beetles, which cover 45-50 percent of the insect world.
 * General :**


 * Sub-Phylum :**
 * Trilobita**: This sub-phylum had been extinct for millions of years. These animals are some of the earliest signs of **Arthropoda** on earth. Dating back millions of years ago, their fossils show us what was once an **Arthropod.**


 * Chelicerata:** The sub-phylum is one of the major subdivisions of the phylum **Arthropoda.** This sub-phylum includes Horseshoe Crabs, Spiders, Scorpions, and Mites. There are over 77,000 identified species of **Chelicerates**, and there may be about 500,000 unidentified species.

This sub-phylum includes familiar groups as barnacles, crabs, crayfish, lobster, water fleas and pill bugs. Crustaceans have a very important role in the food webs of Marine life. There are about 40,000 different species of **Crustacea** in both fresh and salt water all over the world. About 200 species can be found in the great lakes of North America.
 * Crustacea:**


 * Atelocerata:**
 * Atelocerata** is a sub-phylum of **Arthropoda** which includes Milipedes and Centipedes. This sub-phylum excludes crustacea because this is a division where the animals breathe through **Tracheae**(Please scroll up for definition.) instead of gills, like the crustacea.

All species that falls under the phylum of **Arthropoda** have two very distinct characteristic. They all have an exoskeleton, as well as jointed appendages. One exception are wings that some of the **Arthropods** have. Wings do not count as appendages. Though the legs, neck, and head do count. As you can see in the picture below, these two characteristics apply. http://www.ucmp.berkeley.edu/arthropoda/arthropoda.html http://biology.clc.uc.edu/courses/bio106/arthrpod.htm http://www.peripatus.gen.nz/taxa/arthropoda/index.html http://www.insecta.bio.pu.ru/z/nom/Atelocerata.htm http://www.eoearth.org/article/Crustacea http://www.fossilmuseum.net/Tree_of_Life/PhylumArthropoda/Subphylum-Chelicerata/Chelicerata.htm http://www.ucmp.berkeley.edu/arthropoda/trilobita/trilobita.html
 * Characteristics :**
 * External Links:**

"Arhtropoda." //Introduction to Arthropods//. Web. 24 May 2011. "Phylum Arthropoda." //Biology at Clermont College - University of Cincinnati//. Web. 24 May 2011. "Arthropoda." //Chris's No-Frills Home Page//. Web. 24 May 2011. "Atelocerata." //Index//. Web. 24 May 2011. "Crustacea." //Encyclopedia of Earth//. Web. 24 May 2011. "Chelicerata." //Fossils Geological Time and Evolution//. Web. 24 May 2011. . "Intro to Trilobita." //Trilobita//. UCMP. Web. 24 May 2011.
 * Sources:**

Emily Mourraille Alex Parks Taylor Voss
 * Authors:**


 * __ Phylum Arthropoda __**

newmani the fossil evidence of the oldest animal. ||
 * Figure 1Fossil of pneumodesmus

Phylum Arthropoda, or joint legged animals as its meaning states, is the most successful known animal. Being the most successful of animals, they make up nearly seventy five percent of all living and fossilized animals. It is predicted that many species of this phylum still have yet to be discovered in tropic rain forests and other ecosystems that support phylum arthropoda. Ancestral arthropods were the first land animals. The oldest known animal to have lived on land is the arthropod Pneumodesmus newmani. Fossil evidence of this species consists of a single specimen discovered in 2004. Pneumodesmus newmani is classified as a millipede and thought to have lived 428 million years ago, during the Late Silurian Period.


 * __ Characteristics of Phylum Arthropoda __**

Listed below are a few characteristics of the phylum arthropoda:
 * The body structure of phylum Arthropoda is a body segmented with paired appendages that typically function as limbs. The body type is known to be so adaptable to its environment, that phylum Arthopoda can be found in almost any ecosystem.
 * The inner parts of phylum Arthropoda is also segmented. The nervous system is composed by anterior ganglia and paired nerve cords.
 * Phylum Arthopoda has an open circulatory system, moving blood through vessels by usage of regular contractions. The cavity that the phylum Arthropoda facilitates to pump blood and assist internal organs is called the hemocoel.
 * Because of this body cavity, animals of this phylum are coelmates. Coelmates can be described as a group of animals with a cavity filled with fluid in which the digestive system is hung from.
 * Animals in the phylum Arthopoda have a line of symmetry. This symmetry is called bi lateral (//bi= two, latus= side//) symmetry. In basic terms, draw a vertical line splitting it in two and the halves should mirror each other.
 * **When arthropods grow, they must molt their exoskeleton:** Since the exoskeleton of an arthropod is a rigid structure, it must be shed and replaced periodically to enable growth. This shedding process is known as molting or ecdysis and consists of a series of four stages. First, enzymes are secreted that loosen the old exoskeleton layers. Second, the new exoskeleton layers are secreted. Third, the old exoskeleton splits and falls off. Finally, the new exoskeleton hardens and sets.

The phylum Arthropoda has a great number of species. However, to give you an idea of the type of animals in the phylum here are a few examples of animals listed in the phylum Anthropoda.
 * __ Examples of Animals in phylum Arthropoda __**
 * Butterflies
 * Beetles
 * Grasshoppers
 * Spiders
 * Crabs

Crustaceans (Subphylum Crustacea) include about 50,000 species of lobsters, crabs, shrimp, barnacles, brine shrimp and others. Most crustaceans live in marine or freshwater environments but there are also some terrestrial species. Hexapods (Subphylum Hexapoda) are a group of arthropods that includes the insects. The body of a hexapod is divided into three sections, a head, thorax, and abdomen. Myriapods (Subphylum Myriapoda) include about 13,000 species of millipedes and centipedes. Myriapods are terrestrial arthropods that are most abundant in forest habitats. They are notable for their long bodies and for having many
 * __ Classification of phylum Arthropoda __**
 * Anthropod subgroups**: Chelicerates (Subphylum Chelicerata) are a group of arthropods that include spiders, mites, horseshoe crabs, and scorpions. The first evolved about 445 million years ago during the Late Ordovician Period. Chelicerate bodies are divided into two regions, the cephalothorax and the opisthosoma.

Figure 3 This is a classification of phylum Arthropoda

Because this phylum is so populated and broad, there are several ways of classifying the phylum. However the one shown beneath is known to be the most widely accepted classification.

Class [|Branchiopoda] (branchiopods) Class [|Ostracoda] (ostracods) || Class [|Pycnogonida] (sea spiders) ||
 * ** Sub-Phylum ** ||  ** Sub-Classes **  ||
 * ** Sub-Phylum trilobita ** ||  ||
 * ** Subphylum ** [|**Crustacea**] || Class [|Malacostraca] (crabs, krill, shrimp)
 * ** Subphylum ** [|**Hexapoda**] || Class: Insecta(insects) ||
 * ** Subphylum ** [|**Myriapoda**] || Class [|Chilopoda] (centipedes) Class [|Diplopoda] (millipedes) Class [|Pauropoda] (pauropods, pauropodans, and progoneates) Class [|Symphyla] (pseudocentipedes and symphylans) ||
 * ** Subphylum ** [|**Chelicerata**] || Class [|Arachnida] (arachnids) Class [|Merostomata] (horseshoe crabs)


 * __ What Makes the phylum Arthropoda so successful __**

The members of the phylum Arthropoda are so successful for a variety of reasons. One reason is said to be their defense tactics against predators. Often the members of the phylum use methods of camouflage and mimicry. Camouflage hides the organism from an unwanted creature (usually a predator). The hiding creature blends into its environment and remains unnoticed by predators. An animal most known to utilize this method is the butterfly species. Natural selection, of course, favors the butterfly born with this defense tactic. The other tactic mentioned, mimicry, is what it sounds like. Mimicking, a species similar to another, to protect one species, or even both. It is when one species mimics the behavior of another to avoid predators. Natural selection also encouraged this among the phylum. Some arthropods are hermaphrodites, meaning they contain both sexes. It is also believed that animals of this phylum evolved from three different groups. They evolved separately from worm-like ancestors with the exception of trilobites.


 * Arthropods employ a variety of reproductive methods**: All terrestrial arthropods undergo internal fertilization and sperm is usually transferred to the female indirectly. Aquatic arthropods vary in their reproductive methods, with some species using internal fertilization and others external fertilization. Most arthropods lay eggs. Scorpions are the exception to this rule, they incubate their eggs internally and give birth to live young. Some members of this phylum can also reproduce without sexual reproduction causing a “population explosion”.


 * __ Sources: __**

[] “Lab 7: Phylum Arthropoda.” Ohio University.@http://www.biosci.ohiou.edu/introbioslab/bios173/173_7.htm (accessed May 25, 2011) [] Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2008. The Animal Diversity Web (online). Accessed May 24, 2011 at http://animaldiversity.org. [] “Arthropods-Phylum Arthropoda.” AngelFire.@http://www.angelfire.com/mo2/animals1/phylum/arthropod.html (accessed May 25, 2011). [|http://evolution.berkeley.edu/evolibrary/article//arthropods_04] “Bilateral (left/right) Symmetry.” University of California-Berkeley.http://evolution.berkeley.edu/evolibrary/article//arthropods_04 (accessed May 25, 2011). [] Carter, J. Stein. “Phylum Arthropoda.” UC Clermont Biology Page.@http://biology.clc.uc.edu/courses/bio106/arthrpod.htm (accessed May 25, 2011). [] “Phylum Arthropoda.” University of Minnesota.@http://www.entomology.umn.edu/cues/4015/handouts/Orders.htm(accessed May 25, 2011). [] Thomas, C.D. “Introduction to the Arthropoda.” University of California Museum of Paleontology.@http://www.ucmp.berkeley.edu/arthropoda/arthropoda.html (accessed May 25, 2011). [] Deyrup, Mark, Barbra Peckarsky, James A. Cox, and Robert W. Pennak. “Insect Life Forms - Phylums.” Insect Life Forms. @http://www.insectlifeforms.com/Phylums488/JOINTED_LEGGED_ANIMALS_ARTHROPODA_6050_488.aspx (accessed May 25, 2011).