Arthropods


 * Arthropods**

__Digestive system-__ Paired appendages around the mouth are used for collecting and handling food and are usually specialized in accordance with the particular diet of the animal. __Nervous system-__ Their nervous system is "ladder like," with two ventral nerve crods running through all segments and forming two ganglia in each segment. __Body plan-__
 * exoskeleton (a skeleton on the outside of the body)
 * body divided into distinct parts
 * jointed legs and appendages
 * bilateral symmetry (both sides of the body are the same)

__Picture-__

http://www.biologycorner.com/bio1/notes-arthropods.html

__Positive impact on humans__ -link in food chain -pollination, most seed plants would not exist, ~65% insect pol. -human food, specifically crustaceans, several million pounds annually  from Gulf of Mexico alone (primarily shrimp) -silk -spider silk can be stronger than steel of the same gauge. -insectivorous arthropods help control insect pests Ex. lady bug -soil dwelling arthropods scavengers and decomposers  -Esthetic and psychological __Negative impact on humans__ -Ticks -Mites -Mosquitoes -Fleas -Lice; look upon people, their pets and livestock as just another meal (parasitic larva can also be involved)  -Painful bites of stings in self-defense, more people die of bee and scorpion stings than by snakebite (or shark attacks!) __1 interesting fact__ They first evolved about 445 million years ago during the Late Ordovician Period.