Phylum Arthropoda Introduction

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Phylum ArthropodaIntroduction
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ArthropodaGeneral 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

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ArthropodaGeneral Characteristics

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

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ArthropodaGeneral Characteristics

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

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Appendageslots of specialization

• locomotion
• swimmerets
• walking legs
• reproduction
• gonopods

Appendages primitively with one pair per segment
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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

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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

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Respiratory System

• Respiration by
• body surfaces - primitive forms
• gills - crustaceans
• trachea - insects
• book lungs - chelicerates

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Excretion

• Most with with paired glands
• coxal, antennal or maxillary
• insects and others
• malpighian tubules

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Nervous System

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

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Reproduction

• usually dioecious
• usually internal fertilization
• oviparous or ovoviviparous
• often with metamorphosis
• some have parthenogenesis

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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