Arachnid

Author: Megan Porterfield
__**EXAMPLES**__: //**Scorpio maurus palmatus**// Common Names: "North African/Middle Eastern Scorpion" "Long-clawed Scorpion" "Isreali Gold Scorpion"

//**Pholcus phalangioides**// Common Names: "Daddy Long-Legs" "Cellar Spider" "Vibrating Spider"

__**HABITAT**__:
 * almost all arachnids live in terrestrial habitats, few species, including the water spider, live in freshwater and marie habitats
 * arachnids have been know to live in all conditions and habitats; moist and dry environments, cool and hot temperatures, however the greatest and most diverse number of arachnids species thrive in warm, arid, tropical habitats
 * spiders, the most common arachnid, are found in houses in high ceiling corners, in basements, and in cellars

__**TYPE OF COELOM:**__
 * like all arthropods, arachnids have a true, but reduced coelom
 * the coelom is completely lined by the mesoderm layer
 * the internal organs within are complex, and held in place by mesentaries


 * __ENDOSKELETON or EXOSKELETON__:**
 * all arachnids have an exoskeleton, along with an internal support structure made of a material called //endsternite//
 * //﻿//**endsternite**- is a cartilage-like tissue that allows for movement
 * the muscles attatch to this internal support structure, thus allowing locomotion


 * __TYPE OF NERVOUS SYSTEM__:**
 * consists of a brain and a spinal chord- like chain of paired ganglia (nerve bundles)
 * Brain- the large ganglion located above the esophagus
 * nerve bundles that extend upwards from the brain control the eyes and the chelicerae
 * nerve bundles that extend into the abdomen control the pedipalps and legs

__**FEEDER**__: Arachnids are **Predators** and **Liquid Feeders**
 * After catching their prey, arachnids use their chelicerae to puncture the skin of their victim and pour into it digestive juices
 * the digestive juices turn the insides of the prey into a soup-like texture
 * the arachnid then sucks out the 'soup' leaving the rest of the body untouched
 * many sepcies of arachnids produce a type of poison in their chelicerae that they use to paralyze their prey before injecting the digestive juices

__**SYMMETRY**__: Arachnids have **Bilateral Symmetry** a line could be drawn down the middle of the organism, and create two equal halves = bilateral symmetry
 * -** bilateral symmetry means an organism has matching body parts on both the right and left side

__**REPRODUCTION**__:
 * arachnids are single-sex organisms; meaning that each organism has either the female sex organs or the male sex organs, not both.
 * The gonads (sex organs) are located in the second segment of the abdomen
 * Male arachnids pass sperm into female arachnids in packages called //spermatophores//
 * Most arahcnids lay fragile membraneous eggs that hatch young that closely resemble the adult of the species
 * Scorpions however, are viviparous, which means they bear live young
 * Many arachnids have a form of "dating" and practice complex courtship rituals to ensure that the male sperm is delivered into the female
 * In many species of spiders, after mating, the female will eat the male

__**CIRCULATORY SYSTEM**__:
 * arachnids have an open circulatory system that includes: a heart, blood vessels, and hemolymph
 * Hemolymph is pumped from the heart, through the blood vessels, and into tissue sinuses. It then is pumped back into the heart.
 * **Hemolymph** is a liquid substance that contains cells. It does not carry oxygen but **hemocyanin**; the respiratory chemical in arachnids



__**ENDOTHERMIC or ECTOTHERMIC**__. Arachnids are **Ectothermic**
 * "cold-blooded" which means that they cannot maintain their body temperatures internally
 * this also means that arachnids have a low rate of metabolism
 * arachnids are able to maintain their body temperatures by getting heat from their surroundings and by eating other insects

__**SEGMENTATION**__: Arachnids are divided into two segments:
 * 1.) Cephalothorx -** fusion of the cephalon (the head) and the thorax (the chest), covered by one unsegemented carapace (protective shell-like substance)
 * contains the sensory organs, mouthparts, and lims
 * the small, leg-like structures protruding from the cephalon are called **chelicerae**. depending on the species, chelicerae can serve as pincers or poison-containing fangs
 * The first pair of legs are called **pedipalps** and can serve as pincers, feelers, or walking limbs
 * 2.) Abdomen -** usually divided into at least two parts, the preabdomen and postabdomen, but these distinctions are not visible on most species, mainly in scorpions
 * contains the genital opening and book lungs

- all 8 legs are attached to the body at the cephalothorax, not the abdomen
 * Arachnids have four pairs of legs**- having 8 legs is possibly an arachnid's most distinctive feature

__**WORKS CITED**__: "Arachnid (arthropod) :: Circulatory System -- Britannica Online Encyclopedia." //Encyclopedia - Britannica Online Encyclopedia//. Web. 28 Mar. 2011. .

"Arachnids: Pictures, Information, Classification and More." //Everything About//. Web. 28 Mar. 2011. .

"Animal Phyla." //WAYNE'S WORD//. Web. 28 Mar. 2011. .

"The Daddy Long Legs: Spider or Insect?" //Scientific AmeriKen - Regular Milk vs Organic Milk: Finding the Differences - February 2011//. Web. 28 Mar. 2011. .

Platnick, Norman I. (2009): [|The world spider catalog], version 9.5. //American Museum of Natural History//.

Hallan, Joel (2005-03-07). [|"Synopsis of the described Araneae of the world"]. [|Texas A&M University]