ARACHNIDS
GENERAL FEATURES
Class arachnida (Gr. arachne = spider)
This class of organism make up a part of Subphylum Chelicerata of Phylum Arthropoda, and like arthropod, this animals have particular characteristic:
- Bilateral symmetry.
- Hard exoskeleton.
- Jointed appendages for walking.
- Highly developed sensory organs.
- Muscular system complex.
- Segmented o unsegmented abdomen with or without appendages and generally distinct from cephalotorax.
- Respiration by gills, tracheae or book lungs. and excretion by Malpighian tubules or coxal glands.
- Simple eyes.
ARACHNID BODY
Scorpion´s body
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Scorpions body consist of a rather short cephalothorax, which bears the appendages and from one to six pairs of eyes and a claerly segmented abdomen. The abdomen is divided into a broader preabdomen and taillike postabdomen, which ends in a stinging apparatus use to inject venom. Spider´s body |
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| Internet picture |
INTERNAL STRUCTURE
Respiration process
…By means of
- Book lungs. The air enters into a chamber.
- Tracheae. The air enters across opening called spiracles.
- Both.
Excretory system
- Keywords: Malpighian tubules, specialized rectal glands and coxal glands.
- Some waste materials are uric acid and feces.
Spiders..Particular vision
- The “spiders usually have eight simple eyes, each provided with a lens, optic rods and a retina.” (Hickman 2000: 200).
- While some spiders perceive moving objects, others spiders may form images.
- This sense is supported for sensory setae; these structures inform about the surroundings.
