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Introduction to Arthropods
• Most numerous and diverse phylum of animals
• 75% of all animal species
• 1 million known species
• Found in every habitat on earth
• Segmented
• Invertebrates
• Have jointed appendages
• Exoskeleton
General Characteristics• Segments are fused into larger regions
• Each segment has a pair of jointed
appendages (ie. extensions of the
body)
• eg. Antennae, legs
• Functions of appendages:
• Movement
• Reproduction
• Sensory
• Defense
• Gathering food
Exoskeleton• Composed of chitin
• Helps prevent desiccation(drying out)
• Sometimes have a waxy layer
• Makes them waterproof
• Provides support and protection
• Attachment for muscles
• Limits growth
• To grow, they must shed their exoskeleton &
grow a new one (ie. molting)
• Vulnerable when molting
2
3 Subphyla of Arthropods
• Kingdom
• Phylum
• Subphylum
• Class
• Order
• Two pairs of antennae
• Chewing mouthparts
• Legs with claws
• Examples include:
• Lobster
• Crayfish
• Crab
• Barnacles
• Shrimp
1. Subphylum Crustacea
• One pair of antennae
• Chewing mouthparts
• No claws on their legs
• Examples include:
• Insects
• Centipedes
• Millipedes
2. Subphylum Uniramia
• No antennae
• Pincer-like mouthparts
• No claws on their legs
• Examples include:
• Spiders
• Scorpions
• Mites
3. Subphylum Chelicerata
3
� Cephalothorax
� Fused head & chest region to which legs and other
appendages are attached.
� Hard shell (ie. carapace) covers this
� Abdomen
� Long, narrow tail region - divided into seven segments
Crustacean Body Structure Crustacean Systems
A. Respiratory
B. Digestive
C. Circulatory
D. Excretory
E. Reproductive
F. Nervous
A. Respiratory System
• Gills are attached to the walking legs
• Water is pulled up under the carapace during locomotion
• Current of water is sent forward over the gills
• Gills absorb O2 from water and release CO2
• Water exits to the anterior via the second maxillae
• When stationary the gill bailersmove water across the gills so respiration can occur
B. Digestive System• Mandibles crush the food and pass
it on to the stomach
• Stomach pulverizes, strains & sorts food
• Stomach wall has chitinous teeth to grind food
• Smallest particles are sent to the digestive gland for nutrient absorption
• Larger particles are sent to the intestine
• Coarsest particles stay in the stomach to be ground further
• Undigested materials pass through the intestine and out the anus
4
• Open circulatory system
• Heart lies dorsally in a sinus of blood
• Heart has three pairs of openings through which O2
rich blood from the sinus enters the relaxed heart
• Valves close preventing blood from exiting the
openings
• Blood is driven into arteries that go to the tissues of
the body
• O2 deficient blood collects in a large sinus
• It enters the gills to absorb O2 and release CO2
C. Circulatory System
• Solid feces are excreted through the anus
• At the base of the antennae is the green
gland (ie. bladder)
• Regulates the amount of salt and H2O in the
blood
D. Excretory System
• Separate sexes
• Male deposits sperm into a special receptacle near the female pores (ie. where eggs exit)
• Fertilized eggs stick to the abdomen for the months that she carries them
• Crustacean hatches from the eggs as a free-swimming larva
E. Reproductive System
• Similar to annelids
• Brain
• Nerve cord
• Compound eyes
• Composed of hundreds or thousands of closely packed lenses
• Well suited for detecting motion
• Important for hunting
• At Night
• Deep water with very little light
F. Nervous System