Wecht+Arachnid

=**__Arachnids__**= https://docs.google.com/file/d/1H-XMn5QIaaH1pY21-4HLqfgJ1_k7jD6yAl51nH6H9P45lR3IZFrNQcOnPEwq/edit?pli=1
 * __PowerPoint:__**



= = =**SubKingdom: Metazoa **= =**Phylum: Arthropoda**= =**Class: Arachnida**=

All Arachnids have four pairs of legs, making eight in total. However in some forms the upper pair of legs are more for defense or senses. The body is divided into sections, the cephalothorax (2) and the abdomen (3). Arachnids can be differentiated from insects in that they have eight, as apposed to six, legs and that they lack antennae or wings. All Arachnids have a hard exoskeleton of varying thickness and internal cartilage-like tissues that bond to some muscles. Endoderm, Mesoderm, and Ectoderm germ layers
 * __Body plan:__**
 * __ Germ Layers: __**

__** Symmetry: **__ All Arachnids have a bilateral symmetry.

__** Coelomate: **__ Arachnids are from the Arthropod phylum and so have coelomate.

__**Habitat**__: Arachnids are found in many varied environments such dry deserts, underground, damp areas, trees, plant life, and aquatic environments. However the majority of this class live in terrestrial environments.



__** Movement: **__ Many Arachnids can utilize their many legs to latch on to surfaces and climb angles impossible to other creatures. Due to their relatively small size it is common for Arachnids to latch on to fur or clothing of other creatures and utilize them for transportation.

__** Skeletal System: **__ Arachnids have an exoskeleton meaning they have a hard outer layer of bone like substance (chitin) serving much the same function as a skeletal system. The exoskeleton has to layers, a thin outer layer containing a wax to become impermeable to water, and a thick inner layer. Within the body thin membranes are present at every articulation to facilitate movement.

__** Evolutionary Advancement: **__ The most obvious evolutionary advancement is that the majority of arachnids still present are land based. The jointed legs gives them a far greater amount of mobility and speed on land then it does on water. The segmented body has also proved to be useful in that each segment can become individually specialized. The exoskeleton has also grown in thickness to prevent water loss and improve protection.

__** Special Adaptations: **__ Many types of arachnids utilize their eight legs for more then transportation as they often have things such as barbs or spikes on them. These can be used to dig in a material to hang from, to climb on, or to inject something.

Most arachnids are carnivorous, eating pre-digested insects or small animals. Some types of spiders are known to eat their own silk however this is not their sole source of nutrition. The arachnid will first often secrete venom to kill the prey then pour digestive juices over the body, then later returns to “drink” the creature.
 * __Feeding Patterns__**

__** Respiration: **__ The majority of arachnids utilize a spiracle, a hole on their exoskeleton that allows air to enter the trachea. This can be closed or opened to prevent water loss. Book lungs are also used widely. This structure contains stacks of air pockets sandwiched between tissues to facilitate gas exchange.

__** Circulation: **__ The heart, which may or may not be segmented, is located in the upper abdomen. This pumps blood throughout the body which can be oxygenated or not, depending on the efficiency and type of respiration system. Oxygenated blood can contain haemocyanin which is a copper based molecule similar in function to haemoglobin.

__** Excretory: **__ The primary nitrogenous waste for arachnids is guanine. Common excretory glands include coxal glands and Malighian tubules.

__** Nervous: **__ Arachnids have a brain and chains of nerve bundles throughout the body. These bundles make up for the fact that arachnids lack a spinal column. Several of the specialized segments of the body can contain clusters of specialized nerve cells to accomplish a specific task.

__** Reproduction: **__ Arachnids have one to two gonads within the abdomen. Complex mating rituals that can rival those of more complex mammals will result in the male transferring sperm to a female in a spermatophore. These complex rituals ensure safe delivery and reproduction success. Most arachnids will lay eggs, many at a time, that hatch to resemble the adults. Some, such as scorpions, directly give birth to their young.

Info: [] http://www.everythingabout.net/articles/biology/animals/arthropods/arachnids/ http://animals.howstuffworks.com/arachnids http://insects.about.com/od/noninsectarthropods/p/arachnida.htm http://atschool.eduweb.co.uk/sirrobhitch.suffolk/key/spiders.htm

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