General Info

Arthropods can be considered as the most successful phylum of Kingdom Animalia. They have been on the Earth since 600 million years ago. They are found on the terrestrial land, underwater, and even in the air. Arthropods are also known as animals with jointed appendages. Arthro- means joint; -pod means foot. They very diverse and abundant because vary in size, shape,and habits.

They have three important features:

1. A tough exoskeleton:

• made of chitin
• can be leathery and flexible (ie:insects) or hard (ie:crabs)
• provides protection, structure and prevents desecation
• many are waterproof
• cannot grow as the animal grows
• allows movement only at joints
  

2. A series of jointed appendages:

• primitive arthropods (ie:trilobites)= each segment has 1 pair
• as body segments are lost, so are appendages
• modify into antennae, claws, wing, flippers, etc.
  

3. A segmented body:

• some have many (ie: millipede)
• due to evolution, some have little (ie:crabs)
  

Arthropods are divided into 4 subphylums:

1. TRILOBITA:

• the oldest of arthropods
• lived in the sea
• extinct =(
  

2. CHELICERATA:

3 scorpions

• lack sensory "feelers"
• body divided into:
  1. cephalothroax (anterior end)
  --------->contains brain, eyes, mouth, mouthparts, and esophagus
  2. abdomen (posterior end)
  --------->contains most internal organs
• has 2 pairs of appendages by mouth as mouthparts:
  --->1st pair called chelicerae
  --->2nd pair called pedipalps
• ie: spiders, ticks, scorpions

3. CRUSTACEA:

A shrimp

• have stony exoskeleton usually made of calcium carbonate (limestone)
• 1st two pairs of appendages = antennae ("feelers")
  --->contains sensory hairs
  --->used as sense organs or filter feeding
  --->water fleas use them for movement (to push through water)
• 3rd pair of appendages = mandibles (mouthparts)
  --->many are short and heavy: used for biting and grinding food
  --->some are bristly: used for filter feeding, finding food, picking up ditrius
  --->some are needle-like: suck blood from host
• body parts are:
  --->head, thorax, and abdomen
  --->cephalothorax (fusion of head and thorax); covered by tough shell called carapace
• ie: Crabs, shrimp, barnacles

4. UNIRAMIA:


A grasshopper

• largest subpylum of arthropods
• have 1 pair of antennae and appendages
• ie: centipedes, millipedes, and insects
• Centipedes
  --->carnivores (eat earthworms, toads, mice, etc.)
  --->have a pair of poison claws on head
  --->North American can be 3-6 cm long; Tropical can be up to 26 cm long
  --->have 15-170 pairs of legs
  --->1 pair of leg per segment except last 3 segments (which has no legs)
• Millipedes
  --->2 pairs of legs per segment
  --->live in damp places such as decaying logs
  --->eat dead/decaying plant material
  --->for protection, they roll into a ball
  --->some can give off a disgusting odour
• Insects
  --->have 3 body parts: head, thorax, and abdomen
  --->3 pairs of legs attached to thorax
  --->has 1 pair of antennae
  --->has 1 pair of compound eyes
  --->2 pairs of wings found on thorax
  --->uses tracheal tubes for respiration