Phylum Arthropoda: The Arthropods
- Most successful animal group ever to live
- Consists of over 1 million named species, 2 of every 3 animals are arthropods. ~ 1018 individuals.
- Inhabit all ecosystems
- All have a hard exoskeleton
- Composed of protein and chitin
- Allows for great variation in function - biological "swiss army knives"
- Must molt as they grow
- Limits their size
- Have well developed body segments and appendages
- Have well developed sensory organs including true eyes and antennae
- Have open circulatory systems & special gas exchange organs
Subphylum Chilicerata (arachnids, horseshoe crabs & sea spiders)
- Divided into 3 classes; Arachnida, Merostomata & Pycnogonida
- Body divided into 2 regions
- Abdomen
- Cephalothorax (fused head & thorax)
- Lack jaws
- Have 6 appendages & no antennae
- First appendages form chilicerae (frequently fangs)
- Very diverse class
- Most species parasitic or predatory
- Many possess book lungs for gas exchange
- Spiders are able to produce a strong polymer - silk
- Chilicera in form of fangs
Class Merostomata - Horseshoe crabs
- Ancient group of species
- Changed little over 350 million years
- Aquatic, mostly found on Atlantic & gulf coasts of United States.
- Class Insecta (insects)
- Class Chilopoda (Centipedes)
- Class Diplopoda (Millipedes)
- Millipedes (diplopoda) are segmented worm-like animals
- Have 2 pairs of legs per segment
- Primarily herbivores & decomposers
- Centipedes (Chilopoda)
- Usually terrestrial carnivores
- Have 1 pair of antennae
- Are often poisonous, using modified front claws to immobilize prey
- Far & away the most diverse of animal groups
- More types of insects alone than all other animal groups combined
- Inhabit all terrestrial & freshwater ecosystems.
- Success largely attributed to coevolution with flowering plants.
- Insects have 6 legs
- 3 body parts
- Head
- Thorax
- Abdomen
- Most insects have wings, however in many species these are vestigal
- Have advanced excretory system composed of malphygian tubules
- Exchange gasses through a complex tracheal system
- Have complex compound eye which is usually extremely sensitive to motion and allows 3600 vision
- Have specialized jaws/mouthparts suited to their ecological niche
- Most insects undergo a process of metamorphosis - 2 types
- Incomplete metamorphosis
- Larva similar to adult, with differing body proportions
- Undergoes a series of molts resulting in adult phenotype
- Complete metamorphosis
- Larva is very unlike adult phenotype
- Envelopes self in a coccoon or chrysalis where body breaks-down and reforms into adult form.
- Includes crabs, lobsters, crayfish, shrimp, krill & barnacles
- Over 40,000 species
- Appendages are often highly specialized
- Gas exchange is usually through gills
- Many species taste delicious in butter
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