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Animal Diversity > 7. Arthropods 1 > Flashcards

7. Arthropods 1 Flashcards

1
Q
  1. how are arthropods classified? 2
A
  1. arthropoda is a phylum

2. split into 3 subphyla - trilobites, chelicerates and mandibulates`

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2
Q

what adaptations do arthropods have? 6

A
  1. these are crown group features
  2. pronounced tagmatisation
  3. chitin in exoskeleton-muscle fibres can pull against it, allowing fast movement
  4. jointed appendages for rapid movement
  5. complex mouth parts
  6. ventral nerve cord and dorsal donut brain that goes around esophagus
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3
Q

What advantages do the adaptations of arthropods give them? 7

A
  1. chitinisation protects from predators and dehydration
  2. muscle anchor points
  3. possibility of jointed limbs and segments
  4. wade range of feeding habits
  5. rapid movement
  6. hormones control molting of exoskeleton, molting leaves arthropod very vulnerable
  7. 380/90m years ago, movement onto land lead to a total change in the ecosystem eg. plant coevolution and pollination
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4
Q

Describe some early arthropods. 3

A
  1. burgessia has a telson and jointed limbs
  2. noroia
  3. hard exoskeleton
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5
Q

What are trilobites? 6

A
  1. own subphyla. we don’t know their real position on the tree of life.
  2. about 15 000 morphological species
  3. exoskeleton - well preserved
  4. some spp may have been predators, mostly detritivores
  5. 4cm-70cm
  6. marine and benthic or pelagic
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6
Q

Describe trilobite morphology. 7

A
  1. 3 longitudinal lobes - 1 axial and 2 pleural either side
  2. cephalon (head and eyes) hard with freely articulating thorax
  3. fused pygdium with telson
  4. prothorax - legs and spine can curl up
  5. legs are rarely preserved
  6. legs are biramous - 2 branches
  7. outer leg for walking, inner leg for gills for additional o2 absorption
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7
Q

Describe trilobite development. 3

A
  1. anterior-posterior/ A-P body axis
  2. cephalon and pygdium fused
  3. assumed Hox genes involved - similar structure to modern arthropods
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8
Q

What is special about trilobite eyes? 4

A
  1. some have calcite lenses - ca from sea used to make them makes thin sheets of transparent calcite
  2. eyes either holochroal (many small lenses) or schizochroal (few large biconvex lenses)
  3. may have had binocular vision
  4. has a lip to shade eyes near surface so can see predators
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9
Q

How and when did trilobites go extinct? 6

A
  1. no explanation
  2. end of permian as part of the great dying
  3. volcanic atmosphere - climate change?
  4. appearance of predators eg. sharks probably didn’t help
  5. decline began before the end of the cambrian
  6. less diversity and lower numbers
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10
Q

What are the chelicerata? 5

A
  1. 1st pair appendages modified to form mouthparts or chelicerae
  2. padipalps
  3. 4 pairs legs
  4. no antennae
  5. no mandibles
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11
Q

What are the classes of chelicerata and what do they include? 3

A
  1. Pycnogondia/sea spiders
  2. merostomata include eurypterida/extinct giant sea scorpions and xiphosurida/horseshoe crabs
  3. arachnida include araneae/spiders, scorpiones/scorpion, opilliones/harvestmen and acari/mites
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12
Q

Describe the pycnogondia/sea spiders. 9

A
  1. not spiders
  2. large size range, up to 0.75m legspan
  3. found in all seas, esp, polar regions
  4. larvae not planktonic - slow dispersal. lay eggs, move around on floor
  5. no digestive system - sucks up food
  6. may be carnivorous grazers
  7. male ejaculates onto laid eggs, gathers and carried them around in oviger (modified appendages)
  8. may even carry larvae
  9. 3 appendages of larvae correspond to cephalic appendages of adult
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13
Q

Describe the merostomata/sea scorpions. 3

A
  1. not scorpions
  2. cambrian origin, 570m years ago
  3. dominates seas until about 310m years ago
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14
Q

Describe eurypterida/giant sea scorpions. 10

A
  1. largest arthropod, up to 2m long
  2. 4 pairs walking legs
  3. chelicerae and pedipalps
  4. 12-segmented abdomen
  5. telson, sometimes with non stinging spine
  6. found on all continents
  7. trace fossil found in scotland
  8. 330m year old tracks - no associated animal
  9. hibbertopterus - emerged on land
  10. 1,6m long, 1 m wide tracks filter feeder
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15
Q

Describe xiphosurida/horseshoe crabs. 9

A
  1. 3 surviving genera, 4 spp
  2. live in shallow seas around japan and indonesia
  3. mate on beach
  4. females attract males by chemical signals, dig pit for eggs
  5. external fertilisation, can by polyandrous
  6. embryos later released, planktonic, often eaten
  7. eats worms, small molluscs
  8. we have trace fossils that are 150m year old
  9. swept into anoxic lagoon and died there
  10. looks fairly unchanged but some silurian fossils are biramous
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16
Q

Describe xiphosurida morphology. 9

A
  1. not a crab
  2. not a trilobite - has book gills and no 3 lobes
  3. 1 pair chelicerae
  4. 1 pair pedipalps
  5. 4 pairs walking legs
  6. 5 appendages have book gills
  7. limulus genus eyes tested - relatively large compound eyes and only extant chelicerate to have them
  8. blue blood due to copper based hemocyanin
  9. blood used to test for microbes
17
Q

describe the arachnida. 5

A
  1. huge anatomical variation
  2. 2 tagmata - cephalothorax and abdomen, often indistinguishable
  3. book lungs/gill plates
  4. usually have chelicerae, pedipalps and 4 pairs walking legs
  5. usually predators, fangs are modified chelicerae or pedipalps
18
Q

What are the trigonotarbida? 9

A
  1. may be oldest land athropods, about 400m years olg
  2. appear shortly before the true spiders
  3. fossil found in rhynie chert, scotland - previous hot spring area allowing for instantaneous preservation
  4. no spinnerets
  5. externally segmented abdomen
  6. eyes on separate tubercules
  7. 3 species
  8. very small, about 4mm
  9. probably single terrestrialisation event for arachnids
19
Q

Describe the key features of the araneae/spiders. 4

A
  1. 40 000 species
  2. all carnivorous except 1
  3. 2 tagmata - cephalothorax and abdomen
  4. appear about 380m years ago
20
Q

Describe araneae reproduction. 8

A
  1. indirect sperm transfer
  2. male use chelicerae to get sperm from special web, then transfers to female
  3. sperm come from pedipalps
  4. some spp show parenting behaviur
  5. dangerous animals - mating is careful eg. pluck web in certain way to get female attention
  6. web spiders use vibration and pheremones
  7. salticid spiders wave arms and use vibration
21
Q

Describe salticid spiders. 3

A
  1. 2-3mm big
  2. can move their eyes, producing great binocular images. point where photoreceptors are
  3. ambush predators - jump
22
Q

Describe the vegetarian spider. 4

A
  1. salticid - bagheera iciplingi
  2. eats beltian bodies on acacia leaves
  3. acacia protected by ants in classic mutualism
  4. will eat ant larvae sometimes
23
Q

Describe the opiliones/harvestmen. 16

A
  1. short and stubby legs possible. long legs used to feel ahead
  2. usually 1 pair eyes
  3. don’t produce silk
  4. no pedical connecting tagmata - fused
  5. externally segmented abdomen
  6. chelicerae
  7. may use chemical communication - males have enlarged tibia with more pores for glands
  8. known to rub legs together on thighs
  9. about 6000 species known, may be up to 10 000
  10. up to 4000m altitude
  11. nothing known of african, tropical asian or amazonian species
  12. omnivirous or carnivorous, may eat fungus, bananas etc
  13. masticate food ie. chew, don’t spit
  14. XY sex determination
  15. internal fertilisation, male penis is basically an everted version of ovipositor
  16. earliest fossil - about 400m years old, rhynie chert
24
Q

What are the solifugae/solpugida? 3

A
  1. camel ‘spiders’

2. 2 pairs chelicerae - split

25
Q

Describe the scropiones/scorpions. 7

A
  1. 1400 spp
  2. pincers are pedipalps
  3. mating dances
  4. 4 pairs walking legs
  5. spermatophore transferred to female by male pushing her onto it
  6. can lose tail is necessary, doesn’t grow back and anus is at end
  7. fluoresce, like most arachnids
26
Q

Describe whip scorpions/amblypigi. 4

A
  1. 140 spp
  2. not true scorpions, no sting, therefore harmless
  3. first pair of legs modified as sensors
  4. mating as in scorpions
27
Q

Describe the acari/mites. 12

A
  1. 45 000 known species, up to 1m
  2. v small, less than 1mm
  3. found in caves, thermal springs, polar extremes
  4. one family is marine - returned to the sea
  5. mainly parasitic
  6. highly abundant
  7. hexapod larvae, no primary segmentation
  8. adults normallu have 8 pairs legs, but can have 1
  9. may not be monophyletic
  10. halacoroidea found at 3600+ m below
  11. close relatives live at sea edge/brackish tidal pools - did they fall back in?
  12. demodex live on human skin and in hair follicles
28
Q

summarise the Trilobites paper by N. Hughes. current biology. 2008. 4

A
  1. resemble horseshoe crabs but similarities between trilobite antennae and antennae of mandiblr-bearing arthropods eg. myriapods and insects
  2. may indicate trilobite diverged little from arthropod common ancestor
  3. much diversity despite conserved body plan
  4. calcified eyes overcome spatial aberration
29
Q

summarise the Pycnogonids paper by m. cobb in current biology, 2010. 7

A
  1. head region - cephalosoma, has a proboscis and 4 eyes
  2. organ systems displaced into legs
  3. take o2 by absorption
  4. DNA evidence and morphology combined suggests pycnogonids are a sister group to arthropods, not chelicerates
  5. gametes released through gonopores
  6. males have glands that secrete viscous substance to hold fertilised eggs to ovigers
  7. can walk slowly and swim

Animal Diversity (13 decks)

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