1. Arthropods
Chapter 46
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2. Jointed Appendages and Exoskeleton
Arthropods all have jointed appendages.
Rigid external skeleton (exoskeleton).
Protects animal and provides sites for muscle attachment.
Brittle, thus there is a limit to arthropod body size due to exoskeleton thickness.
Estimates of a quintillion insects alive at any one time.
1,000,000 species.
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4. Classification of the Arthropods
Traditional Classification
Three subphyla based on morphology.
Trilobites (extinct)
Chelicerates - (pointed mouthparts,sometimes connected to venom glands)
Mandibulates - (chewing mouthparts, sometimes modified)
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5. Classification of the Arthropods
Doubts About Traditional Classification
Key morphological traits are not as powerful as previously assumed.
Revised taxonomy places insects and crustaceans as sister groups.
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6. General Characteristics of Arthropods
Exoskeleton
Molting (Ecdysis)
Compound Eye-insects
Composed of many ommatidia.
Each covered with a lens and linked to a complex of eight retinal cells and a light sensitive core rhabdom.
Apposition Eyes - Daylight
Superposition Eyes - Night
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7. General Characteristics of Arthropods
Circulatory System
Greatly reduced coelom.
Open circulatory system.
Nervous System
Double chain of segmented ganglia running along the animal’s ventral surface.
Brain appears to be inhibitor rather than stimulator.
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8. General Characteristics of Arthropods
Respiratory System
No single major respiratory organ.
Small branched air ducts - tracheae.
Air passes into trachea through spiracles.
Spiders contain book lungs (series of leaflike plates within a chamber).
Excretory System
Malpighian Tubes
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9. Class Arachnida Major Orders Order Araneae: Spiders
Order Opiliones: Daddy Longlegs
Order Scorpiones: Scorpions
Order Acari: Mites & ticks
Have 2 body sections
One pair of chelicerae & one pair of pedipalps
Four pairs of walking legs.
Most are carnivorous, except for mites.
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10. Class Arachnida Order Opiliones: Daddy Longlegs Acari: Mites and Ticks
Order Scorpiones: Scorpions
Order Araneae: Spiders
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11. Live in deep water, but migrate to shallow water in the spring.
Class Merostomata
Horseshoe Crabs
Ancient Group.
Live in deep water, but migrate to shallow water in the spring.
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12. Body almost entirely cephalothorax.
Class Pycnogonida
Sea Spiders
Very small (1-3 cm).
Body almost entirely cephalothorax.
Completely lack excretory and respiratory systems.
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13. All pass through nauplius larval stage.
Class Crustacea
Most have two pairs of antennae, three types of chewing appendages, and various numbers of leg pairs.
All pass through nauplius larval stage.
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14. Crustaceans Decapods “Ten footed”
Exoskeleton usually reinforced with calcium carbonate.
Most body segments are fused into cephalothorax covered by carapace.
Lobsters and crayfish have swimmers and uropods to aid in swimming, and may have a telson (tail spine).
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15. The Myriapods Diplopoda-millipedes Class Chilopoda-centipedes
Head region followed by many identical body segments.
Two pairs of walking legs per segment, tubular body
Not venomous
Scavengers, herbivores
Class Chilopoda-centipedes
Head and many identical body segments
One pair of walking legs per segment, body flattened
Venomous
Carnivores
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16. Largest group of organisms on earth.
Class Insecta
Largest group of organisms on earth.
More than half of all named species on earth are insects.
Hectare of lowland tropical rainforest is estimated to be inhabited by as many as 41,000 insect species.
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17. Head, Thorax, and Abdomen Three pairs of legs. One pair of antennae.
Class Insecta
External Features
Three body segments
Head, Thorax, and Abdomen
Three pairs of legs.
One pair of antennae.
Modified mouthparts
Solid wings
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18. Internal Organization Tubular digestive system.
Class Insecta
Internal Organization
Tubular digestive system.
Dilute digestive enzymes.
Trachea extends throughout body.
Fat Body for food storage.
Sense Receptors
Sensory Hairs - Linked to nerve cells.
Tympanum - Found with tracheal air sacs.
Pheromones - Communication signals.
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19. Insect Life Histories
Most hatch from fertilized eggs laid outside mother’s body.
Undergo edysis multiple times.
Instars
Metamorphosis
Simple
Nymphs
Complete
Pupa (chrysalis)
Larvae
Controlled by hormones.
Molting hormone (ecdysone).
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