Transcript Phylum Annelida

Phylum Arthropoda
Introduction
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
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
Arthropoda
General Characteristics
• metameric body plan
– divided into tagmata (i.e.,
tagmatization)
– somites fused into functional units
• head
• thorax
• abdomen
– or
• cephalothorax
• abdomen
Appendages
lots of specialization
• locomotion
– swimmerets
– walking legs
• reproduction
– gonopods
Appendages:
primitively with one pair per segment
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
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
Respiratory System
• Respiration by:
–
–
–
–
body surfaces - primitive forms
gills - crustaceans
trachea - insects
book lungs - chelicerates
Excretion
• Most with with paired glands
– coxal, antennal or maxillary
• insects and others
– malpighian tubules
Nervous System
• similar to that in annelids
– dorsal brain (cerebral
ganglia) around esophagus
– double ventral nerve cords
– well developed sensory
organs
Reproduction
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•
•
•
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usually dioecious
usually internal fertilization
oviparous or ovoviviparous
often with metamorphosis
some have parthenogenesis
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