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Animal Diversity > 7. Tardigrades, lobopods and onychopherans > Flashcards

7. Tardigrades, lobopods and onychopherans Flashcards

1
Q

Summarise the relationships between tardigrades, lobopods and onychopherans. 7

A
  1. are ecdysozoa
  2. are closely related to arthropods
  3. tardigrades, lobopods, onychophrans and arthropods together are called the Panarthropoda.
  4. Arthropods are divided according to appendages in segments
  5. the head has chelicerae or mandibles if euarthropod
  6. the head segment appendages are used for classification - number of segments with appendages and the specialisation of appendages
  7. The onychophera are closer to the arthropods, followed by the tardigrades, which split earlier
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2
Q

What are tardigrades? 13

A
  1. 550 species
  2. aquatic
  3. mainly terrestrial living in water films
  4. one order are marine - live on edge of sea
  5. 0.05-1mm long
  6. 4 pairs lobopod type legs with tiny claws
  7. layered, chitinous cuticle with indentations, not segments
  8. muscles can pull against indentations for movement
  9. have malpignian tubules - kidney like, could be for excretion but absent in marine species
  10. moult frequently through mouth opening
  11. Donought brain allowed eosophagous through
    12, ventral nerve cord
  12. leg muscle contraction allows movement
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3
Q

How do tardigrades move? 3

A
  1. Smaller tardigrades show negative response to light
  2. No negative phototaxis but increased negative photokinesis ie. stop moving in the light
  3. No apparent response to gravity
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4
Q

How do tardigrades see? 6

A
  1. Very small eyes
  2. single pigment cell cup - approaching organ
  3. contains photosensory pigments
  4. 1 or 2 sensory cells
  5. homology with other bilaterian eyes unclear
  6. do not appear homologous but repeated evolution - however use same photoreceptors and genes eg. Pax6 so we’re unsure
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5
Q

How do tardigrades live and reproduce? 4

A
  1. often live on moss in water films
  2. sexual repro
  3. pathenogenesis - asexual repro where new come from unfertilised eggs
  4. some hermaphroditic species self fertilise
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6
Q

How do tardigrades eat and sleep? 6

A
  1. Usually omnivorous
  2. some canivores and feed on rotifers etc
  3. have stylet for stabbing prey
    4 carry out cryptobiosis in poor conditions - become tun with barely detectable metabolism
  4. love most of water, from 80=90% water down to 3%
  5. Resist 149-(-272) degreesC (almost absolute zero), alcohol and ether
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7
Q

What is the TARDIS programme? 8

A
  1. Tardigrades in space
  2. in 2008, sent them to space on FotonM3 mission on outside of russian satellites
  3. exposed for 10 days as tun during orbit of earth
  4. exposed to cold, vacuum, UV etc, and very resistant
  5. 60% survive 25 days after return to earth
  6. UV is the harmful bit
  7. candidate for teleportation - physicists can change state of particles from one place to another
  8. they want to work out all molecular connections and transport but huge computer power needed
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8
Q

Talk about tardigrade evolution. 5

A
  1. study used 3 protein coding nuclear genes, but selection pressure is a problem when working out age
  2. divergence of tardigrada and arthropoda, 700-852m year ago, very long time ago
  3. some even diverged before ediacaran - 627-691m year ago
  4. suggests multicellular life may have existed before ediacaran
  5. by definitaion, must have lived in sea - what happened?
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9
Q

What tardigrade fossils do we have? 4

A
  1. Mid-cambrian fossils - 500myr ago
  2. orsten preservation - preserved in a type of limestone called orsten that creates near perfect fossils
  3. they are 3d
  4. dissolve rock with acetic acid
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10
Q

Describe tardigrade development. 6

A
  1. ‘pair-rule’ function - gene (often transcription factor) expressed in alternate segments - is not found in tardigrades but is in arthropods and onychophera
  2. striped neurogenetic expression in embryo
  3. basis of segmentation and neuronal organisation
  4. engrailed (en) is common to all bilateria
  5. Pax 3/7 plays a key role in pair rule in arthropods, which enables segment to know what it will turn into
  6. THIS IS IN ARTHROPODS ONLY
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11
Q

What are lobopods? 6

A
  1. Has various meanings
  2. can mean extinct organisms only
  3. can include extant organisms eg. velvet worms if the writer desires
  4. is counting extinct only, incl. all members of lineage from ecdysozoa to onychophera, tardigrades and euarthropoda, not including the groups themselves
  5. includes a variety of structures eg. triolobites and others
  6. some are euarthropods, some not
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12
Q

What is hallucigenia? 10

A
  1. originally thought to be upside down
  2. armoured lobopod
  3. also thought to be wrong way around due to excreted body contents due to being swuashed
  4. drilled and took sems
  5. has two eyes a left and right
  6. circumoral elements - hard structure around mouth
  7. has aciculae - chitinous support rods
  8. anterior tentacles associated with movement
  9. segmented with different appendages and roles
  10. a xenusian
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13
Q

What did Smith and Caron write on hallucigenia? 6

A
  1. Ancestor of all groups would have shared these characteristics with hallucigenia
  2. important for identifying arthropods
  3. elongated head
  4. paired, simple eyes
  5. buccal chamber
  6. differentiated foregut
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14
Q

What are xenusians? 12

A
  1. 11 species
  2. cambrian
  3. marine
  4. heads/tails need reinterpreting in light of hallucigenia
  5. few similarities to arthropods - polyphyletic?
  6. incl. aysheiea and diania
  7. share more/most similarities with onychophera - no head appendages
  8. terminal claws like onychopherans
  9. no antennaw, like tardigrades
  10. no mud in gut
  11. 220m year difference between marine xenusians and first terrestrial onychopheran fossil
  12. morphological similarities could indicate convergent evolution
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15
Q

Describe the onychophera, or velvet worms. 14

A
  1. antennae
  2. superficial similarity to worms
  3. have 300m year old fossils
  4. terrestrial
  5. have a brain, midgut, ventral nerve cord
  6. 0.3-15 cm lonf
  7. have a slime gland - antennae spray slime at prey
  8. minimal tagmosis, no strict segmentation
  9. unjointed legs (14-43 pairs)
  10. no exoseleton, but chitinous cuticle
  11. Different mandibles to mandibulata
  12. dioecious - male attaches spermatophore to female
  13. 2 australian species lay eggs
  14. remainder are vivparous or oviviparous
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16
Q
  1. How are onychophera distributed? 7
A
  1. 1 order - peripatus
  2. 2 families: peripatidae and peripatopsidae
  3. 110 spp
  4. peripatus are mainly tropical
  5. peripatopsidae and peripatus distribution show ancient gondwanaland distribution
  6. all terrestrial but moist - have open trachae like insects
  7. unknown when they invaded the land and became extinct in the sea
17
Q

What soial behaviour do onychophera show? 4

A
  1. australian velvet worm - euperipatoides rowelli
  2. is a member of perpatopsidae
  3. shows dominant behaviour
  4. allows dominant preferential feeding
18
Q

How is the onychopheran nervous system organised? 4

A
  1. Has ventral nerve cord, antennae and brain
  2. similar to chelicerates
  3. single optic neuropil - synpase dense area, relatively low number of cell bodies
  4. can’t use this to determine common ancestry - could be convergent
19
Q

Describe onychophera phylogeny. 3

A
  1. phylogeny of neuronal organisation suggests onychophera lives within arthropod lineage
  2. anatomical phylogeny problematic
  3. possible convergent evolution
20
Q

Descirbe onychophera eyes. 7

A
  1. very strange, non-compound eyes
  2. some argues it could be an early arthropod eye
  3. most species have eyes
  4. rhabdomeric type - cells contain specialised membrane-rich organelle
  5. no structural/developmental similarities with compound eye
  6. onychopheran eye develops from ectodermal groove like euarthropods ocelli
  7. unclear how many ocelli earliest euarthropods had - possible that a single pair, like onychophera, were present in ancestors.
21
Q

Summarise tardigrades as described in the Current Biology Tardigrades article by Goldstein and Blaxter. 5

A
  1. C. elegans type pharynx, but only 4 pairs legs
  2. rehydration from a tun only takes a few minutes
  3. good for studying development evolution as have features of Drosophila and C. elegans
  4. Early cleavages are complete, unlike in Drosophila
  5. Have Hox genes sequenced
22
Q

Summaries segmentation as described in the 2011 current biology article ‘segmentation in animals’ by S. Blair. 6

A
  1. in Drosophila, segmentation occurs when transcription factors are passed through cytoplasm in syncytial blastoderm
  2. AP axis divided into Gap domains, then pair-rule domains, then parasegments, then more domains
  3. vertebrates have no syncytial stage
  4. some arthropods differ and form segments after cells
  5. some think segmentation evolved 3 times - in chordate, annelid and panarthropod ancestors
  6. others disagree due to molecular similarities, think there was a segmented ubilaterian
23
Q

Palaentological and molecular evidence linking arthropods, onychopherans and other ecdysozoa. g. edgecomb. 2009.

Describe the evidence to support both the articulata and the ecdysozoa hypotheses. 4

A
  1. arthropods closer to nematodes and other non-segmented worms than annelids
  2. arthropods closest living relatives are onychopherans and tardigrades
  3. ecdysozoa as a group supported by molecular evidence from many sources
  4. however, the proposed coelmata group incl. arthropods, but not nematodes, splitting up ecdysozoa
24
Q

Palaentological and molecular evidence linking arthropods, onychopherans and other ecdysozoa. g. edgecomb. 2009.

What is EST data and what does it suggest about arthropod phylogeny? 3

A
  1. Expressed sequence tags allow reconstruction of evolutionary relationships based on short fragments of 1000s of genes
  2. this data suggests onychophera are closest group to arthropoda
  3. tardigrades are closer to nematodes, thus confirming ecdysozoa
25
Q

Velvet worms. Blaxter and Sunnucks. 2011. Current Biology.

Describe velvet worms. 4

A
  1. Terrestrial, many legged carnivores
  2. No exoskeleton or jointed limbs
  3. sensory antennea and small eyes
  4. live in damp temperate or tropical forest - poor water holding capacity
26
Q

Velvet worms. Blaxter and Sunnucks. 2011. Current Biology.

How do velvet worms catch prey? 2

A
  1. patrol at night

2. have slime glands below antannae that squirt to capture prey - worm its prey and glue.

27
Q

Velvet worms. Blaxter and Sunnucks. 2011. Current Biology.

How do velvet worms breed? 5

A
  1. Sexually reproducing
  2. Diverse mating and gestation strategies
  3. development takes one year
  4. some non-oviporous care for young
  5. social behaviour and hierarchy exists
28
Q

Velvet worms. Blaxter and Sunnucks. 2011. Current Biology.

What do velvet worms tell us about arthropod evolution? 3

A
  1. Mix of segmented and non-segmented features
  2. Very different development
  3. No segmented ganglia
29
Q

Lobopodians. J. Ortenga-Hernandez. current biology. 2015.

What are lobopodians? 4

A
  1. about 30 species of extinct, soft-bodied animals
  2. like worms with legs, resembling tentacles
  3. not jointed
  4. legs end in hardened claws
30
Q

Lobopodians. J. Ortenga-Hernandez. current biology. 2015.

What was the lobopodian lifestyle like? 4

A
  1. Benthic and marine
  2. crawled/climbed
  3. hardened plates/spines suggests had predators
  4. deposit feeders (detritivores)
31
Q

Lobopodians. J. Ortenga-Hernandez. current biology. 2015.

What is the wider significance of lobopodian research? 4

A
  1. related to panarthropoda
  2. armoured - onychopheran ancestors
  3. those with pair of frontal appendages - euarthropoda ancestors
  4. onychopherans and tardigrades sometimes called extant lobopodians

Animal Diversity (13 decks)

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