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Animal Diversity > 5. Bilateria > Flashcards

5. Bilateria Flashcards

1
Q

What are the main characteristics of the bilateria? 9

A
  1. bilateral symmetry - left and right separated, almost symmetrical 2. beneficial for sensory organs - allows orientation 3. asymmetry around other axies eg. cephalisation and dorsal/ventral asymmetry 4. bilateral symmetry is insignificant compared to asymmetry 5. these structural differences occurred around the same time, evolutionarily. 6. almost all have a flow through gut 7. usually triploblasts - have mesoderm 8. usually have 7/8 hox genes 9. these things offer similarities and advantages in evolution and development
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2
Q

what is the significance of the bilateria? 5

A
  1. evolution of bilaterial symmetry is very important 2. 99% described species are bilaterians, although there is an ascertainment bias as people find them more interesting 3. still most abundant 4. more complex structures, diverse morphology and ecology and radially symmetrical animals
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3
Q

Describe bilaterian development. 5

A
  1. urchins and starfish are classed as bilaterian, even though the adults are radially symmetrical 2. this is because their young are bilaterally symmetrical 3. development has an evolutionary aspect 4. karl grobben, in 1908, found that at the blastula stage, the blastopore becomes either the mouth or the anus 5. this depends on species, and is significant in classification
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4
Q

describe the old protostome vs deuterostome classifcation. 5

A
  1. used until recently 2. protostomes develop mouth first 3. deuterostomes develop anus first 4. this was original criteria, but the molecular data suggests it is more complex than this 5. protostome is no longer widely used
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5
Q

what are deuterostomes? 5

A
  1. this term is still used 2. includes chordates, hemichordates and echinoderms 3. anus develops before mouth 4, monophyletic 5. closer to each other than other groups and have traits others do not share
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6
Q

What are the problems with the term protosome? 3

A
  1. arrow worms and lophophorates develop anus first, but are classed as protostomes 2. platyhelminthes don’t have mouth and anus, therefore no flow through gut 3. some protostomes show amphistomy - when mouth and anus develop at the same time
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7
Q

What are the differences between ‘protostomes’ and ‘deuterostomes’

A
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8
Q

what are the modern clades of bilateria? 3

A
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9
Q

descibe trochophore larvae. 3

A
  1. free swimming
  2. float as embryod develop
  3. several bands of cilia around middle
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10
Q

What makes up the lophotrochozoa tree? 5

A
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11
Q

what makes up the ecdysozoa tree? 5

A
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12
Q

describe non-deuterostome olfactory receptors. 3

A
  1. lonotropic receptors are a class of newly discovered receptors in flies
  2. no deuterostomes have these
  3. ecdysozoa and lophotrochozoa do, so must have evolved after the split
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13
Q

what questions remain about bilaterian evolution and what are some possible answers? 7

A

1, is the bilaterian brain homologous?

  1. echinodrms (deuterostomes) have no brain
  2. unclear whether it was lost or early ancestor had none and it evolved twice
  3. What came before protostome/deuterostome split?
  4. what did the earliest bilaterian look like?
  5. how did it evolve from radially symmetrical organisms like cnidarians?
  6. genetic evidence being used to trace back
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14
Q

what is the planuloid-acoeloid hypothesis? 5

A
  1. the first bilaterian was similar to modern acoels
  2. dibloblast radiata eg. cnidarian evolved to triploblast bilateria
  3. non-segmented and acoelmate
  4. this split into two - protostomes and deuterostomes
  5. can be segmented and coelmate
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15
Q

What are acoels? 9

A
  1. small, less than 15mm, soft bodied, unsegmented worms
  2. marine
  3. found worldwide
  4. about 400 species
  5. no gut or coloemic cavity
  6. mouth, syncytial digestive system - cell absorbs food from mouth
  7. primitive deuterostomes
  8. stratocystin head used to sense gravity and cilia to move
  9. patches of eye cells in many species at one end, tendancy towatds cephalisation
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16
Q

where do acoels sit in the tree of life? 3

A
  1. the planuloid-acoeloid hypothesis puts acoels at bilaterians, before protostome/deuterostome specialisation
  2. newer research suggests they are deuterostomes that have lost ancestral features
  3. this seems more likely
17
Q

how do acoels reproduce and develop, and what are their habits? 8

A
  1. hermaphrodites with internal fertalisation
  2. highly developed copulatory organs
  3. mutual copulation (mate with each other)
  4. unique duet spiral cleavage in embryonic development, usually lophotrophozoic trait but not here - part of reason for suggestion as ancestor
  5. can show budding
  6. some live in complex symbioses with algae - algae can live inside
  7. related to nemertodermatids
  8. acoels and nemertodermatids = acoelmorpha
18
Q

What are platyhelminthes? 9

A
  1. defining phenotype are unclear but dna evidence makes sense
  2. don’t fit easily into lophotrochozoa
  3. one internal space with digestive cavity, no coelom
  4. beginning of organ level specialisation eg. eyespots grouped
  5. most developed have 2 ventral nerve cords - ours is dorsal to prevent confusion wtih gut
  6. absorb food
  7. many are parastic
  8. includes planaria, which can regenerate
  9. usually marine but can live on land in humid tropics
19
Q

give a basic deuterostome family tree. 5

A
20
Q

what are the classes that belong to the phylum echinodermata? 6

A
  1. asteroidea/starfish
  2. holothuroidea/sea cucumber
  3. ophiuroidea/brittle star
  4. echnoidea/sea urchins
  5. concentricycloidea/sea dasies
  6. crinoidea incl. sea lillies
21
Q

What are the echinodermata? 9

A
  1. 5/6 extant cladees - crinoids?
  2. phylogenetic relations of the remainder still disputed
  3. larvae are bilaterally symmetrical, not adults
  4. many adults show radially symmetry - derived character
  5. 2 sexes - ecternal fertilisation
  6. coelomate
  7. distributed nervous system
  8. no brain or specialised sense organs
  9. have neruons eg. starfish/asteroidea have eye cells at end of feet for movement navigation
22
Q

Describe the sea pigs, class holothuroidea. 5

A
  1. genus scotoplanes
  2. abyssal depths - 6000m deep
  3. found in groups, possible social behaviour
  4. detritivores
  5. gastropod parasites burrow into them and eat them
23
Q

describe the hemichordates, phylum hemichordata. 4

A
  1. look like chordates, with gill slits and notochord
  2. notochord is not homologous with ours, although they are close relatives
  3. sedentary/sessile marine animals or burrow
  4. incl. acorn worms
24
Q

describe hemichordate phylogeny. 3

A
  1. morphologically, they appear more closely related to chordates than echinoderms
  2. molecular data reveals they are actually more closely related to echinoderms
  3. echinoderms lost the notochord
25
Q

Describe the salp tunicate.

A
  1. in the phylum chordata.
  2. planktonic
  3. contracts - uses this to move/feed
  4. some crustaceans live inside them
  5. as larvae, have heart, gonads, stomach and notochord
  6. strange life cycles - can be colonial and reach huge sizes
  7. genetic data and full life cycle infovare importnat for classification
26
Q

draw a deuterostome family tree. 7

A
27
Q

bourlet and hejnol. acoels. current biology. 2009.

What are acoels? 4

A
  1. no excretory or vascular system
  2. prey on unicellular algae
  3. have a nerve ring brain eith 3-6 extending nerve cords
  4. one of simplest brains and nervous systems in bilateria
28
Q

bourlet and hejnol. acoels. current biology. 2009.

How do acoels reproduce? 3

A
  1. very developed copulatory parts
  2. sperm have 2 flagella, only one other group has this
  3. some species use hyperdermic insemination - sperm injection
29
Q

bourlet and hejnol. acoels. current biology. 2009.

what is the acoel’s habitat? 3

A
  1. are meiofauna
  2. some live as commensals with invertebrates and corals
  3. some are pelagic
30
Q

bourlet and hejnol. acoels. current biology. 2009.

describe acoel symbioses. 2

A
  1. some have relationships with algae
  2. as adults, entirely dependent on photosynthetic products
31
Q

bourlet and hejnol. acoels. current biology. 2009.

describe acoel phylogenetics. 4

A
  1. originated before most recent common ancestor of bilaterians
  2. base of bilateria
  3. may resemble common bilateria ancestor but shares many traits with cnidarians eg. no flow through gut
  4. primitive immune system that may explain more complex systems
32
Q

summarise the article a can of worms by a maxmen, 2011, nature. 4

A
  1. acoels have no coelom but do have a 3rd tissue layer, suggesting intermediate form
  2. some evidence suggests deuterostomes have acoels and they have just lost many features
  3. have microRNA unique to deuterostomes
  4. however, this may have originated earlier and been lost in all but deuterostomes
33
Q

summarise the article planarians by a. alvarado in current biology, 2004. 4

A
  1. no coelom but have derivatives of endoderm, ectoderm and mesoderm
  2. organ systems
  3. sexual or asexual reproduction
  4. have cells called neoblasts that are regarded as cells and research done on

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