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22 Cards in this Set
- Front
- Back
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Arthropods
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Body in chitinous exoskeleton
Growth by moulting Segmented with pair of appendages on each Limbs modified for tasks (tagmatisation) Head: pair compound eyes, 1+ single-lensed simple eye Paired ventral nerve cords Ganglion in each segment Body circulation open, haemocoel |
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5 subphyla
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Trilobitomorpha: extinct
Cheliceriformes: celicerates Crustacea: crustaceans Insecta/hexapoda: insects Myriapod: centi/millipeded |
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Merostomata
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Cheliceriformes
Horse shoe crabs: 6 marine species |
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Arachnida
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Cheliceriformes
Diverse, long marine fossil record Spiders, ticks, mites Uropygids: whip scorpions Pseudoscorpions Opilione: harvestmen |
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Pycnogonida
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Cheliceriformes
Sea spiders Morphologically conserved All marine Predatory on sponges and cnidarians |
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Eurypterida
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Cheliceriformes
Sea scorpions Many species, marine, freshwater and amphibian Permian mass extinction |
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Myriapoda
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Carnivorous centipedes and herbivorous millipedes
Similar segments Not diverse |
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Crustacea
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Greatest arthropod diversity
Greatest biomass Krill, copepods |
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Hexapods
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Insects
Low morphological diversity Huge species richness Few marine |
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Arthropod body plan
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Tergite plates of exoskeleton
Muscles above legs control via 'pulleys' Heart beats forwards Cuticle with mineral deposit, layers stop brittleness, strong but not heavy Single lens eye: forward/back to focus Compound eyes developed early in arthropod diversification |
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Arthropod cuticle
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Waxy epicuticle
Pores for wax secretion, taste and smell Hairs for contact and vibration detection Waterproof and hard Low water loss Replacement of wax may be reason for moulting Innervated areas for detection of stress |
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Arthropod limbs
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2 branches: biramous, 1 gill and 1 for walking
Ancestral plan Most terrestrial groups uniramous (1 branch) Middle: movement, gas exchange Insect wings from gill-like branches on thoracic limbs Posterior: gas exchange, ancestral gill Chelicertates internalised lungs form book gills, highly modified limbs |
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Gnathobases in trilobites
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Catch prey between them
Pass long Breaks up food Ingests at front |
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Tracheal systems
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Insects, millipedes and some spiders
Novel gas exchange systems Fine branching airways (tracheae) entering body through spiracles |
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Diversity and abundance of arthropod groups
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Crustacea and chelicerates most diverse morphologically
Crustaceans greatest biomass Insects most species, very few in sea Myriapods low morphological diversity/abundance/biomass Answers more likely to be in differences than similarities |
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Age to explain arthropod success
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Morphological differences
Crustaceans and chelicerates more diverse and older than insects Myriapods: ancient, low diversity Insects: youngest, richest |
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Morphological potential to explain arthropod success
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Lineages with more segments to modify able to have more diversity?
Crustaceans/Chelicerates: many, diverse Myriapods: many, morphologically same through time Insects: fewest, most species |
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Why do insects have most species?
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Richness driven by nice availability
Same niche by different species in different places Herbivores in ocean capture algae and select by size, broad diet and fewer niches Plants on land more structurally complex, more niches, many have specific toxic chemical defences Same with plant-feeding mites Host-plant specificity: drives speciation in associated insects and mites |
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Crustacea on land
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Common but not diverse
Dead plant material or fruits without chemical defences No detox metabolism No co-evolution |
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Benefit of flight in insects
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Allows exploitation of small and patchy niches
Female mosquitoes move easily between flower/host and egg laying sites |
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Metamorphosis and niches
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Allows adults and larvae to occupy different niches
Hemimetabolous: continuous change Holometabolous: more dramatic change Zygote - young larva - terminal larva - pupa - adult |
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Marine insects
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Halobates: 5 species, pond-skaters
Pontomyia: midge Bledius spectabilis: intertidal beetle Can live in salt, wings appropriate? Can't metamorphosise or pupae? Can't be permanently aquatic? Crustacea already there and better suited? |
