1. Phylum Arthropoda Introduction

2. Arthropoda General Characteristics
Largest phylum of animals
Over 900,000 species described
includes:
spiders, scorpions, mites, ticks
insects, millipedes, centipedes
crabs, shrimp, lobsters, crayfishes
very adaptive - found in virtually every habitat

3. Arthropoda General Characteristics
When compared to annelids
both are metameric
primitively have single pair of appendages/segment
nervous system along the same plan
similar embryonic development

4. Arthropoda General Characteristics
metameric body plan
divided into tagmata (i.e., tagmatization)
somites fused into functional units
head
thorax
abdomen or
cephalothorax

5. Appendages lots of specialization
locomotion
swimmerets
walking legs
reproduction
gonopods
Appendages:
primitively with one pair per segment

6. Exoskeleton made of protein, lipids, chitin, calcium carbonate
advantages:
protection
fights water loss; most successful terrestrial invertebrate group
allows for effective movement on land
disadvantages
heavy and bulky
needs to be periodically replaced (i.e., molting)
vulnerable during molting

7. Selected System Summaries
Complex muscular system that is segmentally arranged
Reduce coelom; mostly a hemocoel filled with blood
Complete digestive tract with mouthparts as modified appendages
Open circulatory system with dorsal contractile heart

8. Respiratory System Respiration by: body surfaces - primitive forms
gills - crustaceans
trachea - insects
book lungs - chelicerates

9. Excretion Most with with paired glands insects and others
coxal, antennal or maxillary
insects and others
malpighian tubules

10. Nervous System similar to that in annelids
dorsal brain (cerebral ganglia) around esophagus
double ventral nerve cords
well developed sensory organs

11. Reproduction usually dioecious usually internal fertilization
oviparous or ovoviviparous
often with metamorphosis
some have parthenogenesis

12. WHY ARTHROPODS ARE SO SUCCESSFUL?
versatile exoskeleton
segmentation and appendages for efficient locomotion
air piped to cells directly (insects)
highly developed sensory organs
complex behavior patterns
reduced competition through metamorphosis