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Animal Diversity > 4-5: The Cambrian Explosion, Bilateria > Flashcards

4-5: The Cambrian Explosion, Bilateria Flashcards

1
Q

What’s the main group of diversity?

A

Bilateria

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2
Q

Features of bilateria

A

Bilateral symmetry (left and right side), triploblastic (endoderm, ectoderm and mesoderm), have cephalisation (concentration of sensory structures in a head)

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3
Q

What are the three groups in bilateria?

A

Lophotrochozoa (molluscs, annelids, brachiopods), Ecdysozoa (nematodes, arthropods), Deuterostomata (echinoderms, chordates)

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4
Q

When did fish, molluscs and coral appear?

A

Silurian

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5
Q

Who discovered the Burgess shale?

A

Charles Doolittle Walcott

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6
Q

What is special about the Burgess shale?

A

Exceptional preservation of soft tissue, lots of invertebrate fossils eg trilobites, arthropods

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7
Q

How many modern phyla are there?

A

Around 30

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8
Q

How many uninterpreted phyla have been found in the Burgess shale?

A

15-20

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9
Q

Total group definition

A

Living representatives and all extinct relatives of a group

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10
Q

Crown group definition

A

Just the living representatives of a group and closely related

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11
Q

Stem group definition

A

Extinct organisms only, more closely related to the most recent common ancestor than any living representative

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12
Q

Are there more stem or crown group representatives in the Burgess shale?

A

Stem- very few are crown

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13
Q

Waptia features

A

Antennae, eyes, specialised legs, a crustacean- a crown group!!

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14
Q

Anomalocaris features

A

Large claws, disc mouth, swimming fins, a ferocious predator, stem arthropod

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15
Q

Ancient Deuterostomata (earliest evidence for us)

A

Pikaia and Metaspriggina

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16
Q

Pikaia features

A

Notochord, muscle bands

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17
Q

Metaspriggina features

A

Closer than pikaia, notochord, muscle band, paired eyes, Gill arches

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18
Q

How does the Burgess shale overcome preservation bias?

A

Can see soft animals too, not just biomineralising ones with a hard shell/skeleton, so can see more complex food webs and work out relative species balance based on how many specimens of which type we find

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19
Q

What is Chengjiang?

A

Similar to the Burgess, but in China, different species found (eg. no nematodes in Burgess), but some overlap

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20
Q

What is disparity?

A

The variation of species

21
Q

Why was Burgess so good for preservation?

A

Deep sea bed was rapidly buried by fine sediment, possibly by the collapse of a sea cliff. This starved the organisms of oxygen and preserved carbon films, which metamorphosed. Low sulphur and high alkalinity enabled preservation. The window for preservation closed after the Cambrian. Different places give rare insights of an era

22
Q

What’s the current sister phylum to all animals?

A

Ctenophora

23
Q

What symmetries do bilaterians have?

A

Left/right, anterior/posterior, dorsal/ventral

24
Q

What is gastrulation of the blastula?

A

One layer of cells becomes more

25
Q

What is a blastula?

A

A recently fertilised ball of cells

26
Q

What is the cnidarian endoderm homologous to?

A

The bilaterian mesoderm

27
Q

3 main superphyla of bilateria

A

Spiralia (including lophotrochozoa), Ecdysozoa (arthropods etc), Deuterostomia (verts etc)

28
Q

Which main superphyla are Xenacoelomorpha in?

A

None- they don’t fit into any!

29
Q

What make up Xenacoelomorpha?

A

Composed of acoela (flatworm type things) and xenoturbella (simple sacs, difficult to place into anything).

30
Q

Xenacoelomorpha features

A

Have nerves, but no anus, respiratory/circulatory system, or nephridia (kidney type organs). Have a proper mesoderm, but no proper coeloms like most bilaterians

31
Q

What is a coelom?

A

A body cavity filled with water, basically a gap. It is a more complex body plan

32
Q

What is acoelomate? + Example

A

Lacking a coelom cavity eg. Flatworms

33
Q

What is pseudocoelomate? + Example

A

Fluid filled cavity around the gut, eg. Nematodes

34
Q

What is coelomate? + Example

A

Fluid filled cavity within the mesoderm, eg. Annelid worms

35
Q

2 divisions of bilateria based on development of the gastrula

A

Protostomia (Spiralia and Ecdysozoa) and Deuterostomia

36
Q

Protostomia features

A

Mouth is the first invagination during gastrulation, anus is second. Removal of one cell = cell death (called determinate and mosaic). Spiral cleavage of the blastomere. Eg. Wasps, octopus

37
Q

Deuterostome features

A

Anus is the first invagination during gastrulation, mouth is the second. Removal of one blastomere cell = 2 embryos… Twins! (Indeterminate and regulative). Radial cleavage of the blastomere. Eg. Fish, starfish

38
Q

What are most Spiralia?

A

Lophotrochozoa

39
Q

What are platyhelminthes?

A

Flatworms, simple Spiralians. Hermaphrodites, do penis fencing where they try and be the male when mating

40
Q

Distinguishing features of lophotrochozoa

A

Lophophore (ring of ciliated feeding tentacles), trochophore (larvae with characteristic bands of cilia)

41
Q

Examples of lophophorata

A

Bryozoa, Brachiopoda

42
Q

Ecdysozoa features

A

Lack a spiral cleavage, periodic moulting of the cuticle, three layered cuticle. Include arthropods and friends

43
Q

Deuterostomia features

A

Defined by blastula development, notochord, include us!

44
Q

3 types of Deuterostome

A

Hemichordates, Echinoderms, Chordates

45
Q

Hemichordate features

A

Burrowing marine worms with gill slits and a stomochord, eg. Acorn worms

46
Q

Echinoderm features

A

Pentaradial symmetry, vascular water system, eg. Starfish

47
Q

Chordate features

A

Vertebrates and our invertebrate relatives, eg. Us

48
Q

What are Anbulacaria?

A

Echinoderms + hemichordates

49
Q

Homologous features between chordates and hemichordates

A

Body axis formation and organisation, pharyngeal gill slits

Animal Diversity (12 decks)

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