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ZOOLOGY 300 > Week 3 > Flashcards

Week 3 Flashcards

1
Q

Is Ctenophora the sister group to the rest of the Animals?

A
  • Highly debated
  • Increasing support in genome-scale phylogenetic studies
  • Some recent phylogenies still disagree and claim sponges are the sister group to animals (Ctenophore-first phylogenies suffer from systematic errors called long branch attraction)
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2
Q

Long branch attraction

A

Long-branch attraction occurs when two very divergent taxa or clades with long branch lengths (i.e., many character changes occurring over time) are inferred as each other’s closest relative due to convergent evolution of a given character (e.g., amino acid substitution), and is a common problem in parsimony

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3
Q

Difficulties placing Ctenophora

A
  • Implications for evolution of the CNS
  • If Ctenophora is the sister group to the rest of animals (Ctenophores first) … did the central nervous system evolve twice or did sponges lose the central nervous system
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4
Q

Gastrulation

A

Cells in one region of the blastula begin to involute, forming a cavity called the archenteron

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5
Q

Layers of Gastrula

A

Outer layer: ectoderm
Inner layer: endoderm

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6
Q

Mesoderm

A

After gastrulation, a middle layer of cells forms from the endoderm

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7
Q

Mesoderm in Dipoblastic animals

A

The mesoderm is highly reduced or absent

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8
Q

Mesoderm in tripoblastic animals

A

All three tissue types are present

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9
Q

Schizocoely

A

The process protosomes experience of mesoderm forming from dividing cells in the space between the endoderm and the ectoderm

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10
Q

Enterocoely

A

The process deuterosomes experience of mesoderm forming from pouching of the endoderm (archenteric pouching)

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11
Q

Role of the three germ layers

A

These give rise to different tissue types
Ectoderm- outer surface, CNS, neural crest
Mesoderm- Muscle, red blood cells, bone tissue
Endoderm- Stomach cells, thyroid cells, lung cells

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12
Q

Bilateria

A
  • A clade of bilaterally symmetrical animals that have three germ layers (tripoblasty)
  • Only bilaterians have an anterior brain (cephalization) at some point in development and two types of musculature (ring and longitudinal)
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13
Q

Xenacoelomorpha consists of three groups

A
  • Acoela
  • Nemertodermatida
  • Xenoturbellida
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14
Q

Acoela (Xenacoelomorpha)

A
  • Triboblastic (three germ layers) acoelomates (lack body cavity, the coelom)
  • Absense of excretory organs
  • Body covered in locomotory cillia
  • Lack of defined/complex digestive cavity
  • nervous system consists of commissural anterior brain and 3-5 pairs of radially arranged nerve cords; lack of orthogonal nervous system
  • Statocysts with one statolith and two parietal cells
    -sperm with two flagella
  • direct development
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15
Q

Convoluta roscoffensis

A

Acoels

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16
Q

Acoela and platyhelminths

A

Separate! Not the same

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17
Q

Lack of orthogonal nervous system in acoels

A
  • The nerve cords are transversely connected by an irregular network of fibers (nerve net)
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18
Q

Nemertodermatida (Xenacoelomorpha)

A
  • Tripoblastic (they have three germ layers) acoelomates (they lack a body cavity, the coelom)
  • Absense of excretory organs
  • Body covered by locomotory cilia
    -Distinct gut lumen with simple pharynx
  • Statocysts with two statoliths and several parietal cells
  • Uniflagellate sperm
  • Also once thought to be simplified platyhelminths
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19
Q

Xenoturbellida (Xenacoelomorpha)

A
  • 1 genus, now with 6 species
  • Tripoblastic acoelomates
  • Absense of excretory organs
  • Body covered in locomotory cilia
  • simple ventral oral pole that leads into sac-shaped gastric cavity
  • Nervous system consisting of an intraepidermal net of nerve cells and processes; no ganglia
  • single statocyst
  • uniflagellate sperm
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20
Q

Phylogenetic positioin of Xenoturbella

A
  • basal platyhelminths
  • basal metazoan
  • related to deuterostomes
  • basal deuterostome
  • basal bilaterian
  • protobranch mollusk
  • uncertain kinship
  • related to acoelomorphs
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21
Q

Xenacoelomorpha

A

-Bilaterally symmetrical animals
- Commissural brain with pairs of radially arranged. longitudinal nerve cords (nerve cords connected by an irregular network of transverse nerve fibers)
Lack through gut and nephridia (excretory organs)

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22
Q

Why is Evolution not always parsimonious

A

Because character state changes are not always equally probable (transitions vs. transversions)

23
Q

Long branch attraction (LBA)

A
  • A systematic error where terminals with long branches are erroneously placed together
  • Parsimony approaches are highly prone to LBA and suffer from the condition of statistical inconsistency (as more data accumulates, support increases for the wrong answer)
24
Q

Longer branches

A

More prone to convergence/homoplasy (same character states on terminals, but not because of homology). Parsimony is easily confounded by long branches

25
Q

Why are some branches longer than others

A

Faster evolution (more changes per length of molecular sequence) due to
- Decreased selection
- Increased mutation rate
- Shorter generation times

26
Q

Model based statistical approaches

A

maximum likihood and Bayesian inference
- can mitigate LBA
- extreme cases that violate the model will still be prone to LBA

27
Q

Ctenophores and Metazoa

A

Ctenophores may be the sister group of the remaining metazoa but this placement is not fully resolved

28
Q

Bilateria

A

Animals that possess bilateral symmetry and a mesoderm (middle layer tissue)
three big groups (xenacoelomorpha, protostomia, deuterostomia)

29
Q

Xenacoelmorpha

A

Acoela, nemertodermatia, xenoturbellida
- Bilaterians that lack extratory organs and have an irregular network of neurons

30
Q

Long branch attraction

A

systematic artifact where fast-evolving lineages artificially group together in a phylogeny

31
Q

Root of animal tree of life

A

Porifera, Placozoa, Cnidaria, Ctenophora

32
Q

Symmetry

A
  • Simplest form is spherical symmetry
  • Radial symmetry occurs when organism as a body axis or polarity
33
Q

Poles of body axis in radially symmetrical animals

A

Oral pole and aboral pole (oral-aboral axis)

34
Q

how common is perfect radial symmetry

A

rare in nature (starfish)

35
Q

Biradial symmetry

A

Symmetry down the middle (human, fly,..)

36
Q

Placozoa

A

-Flat organism
- two cell layers
- small genome
- no gut, lower layers of cells absorb food particles

37
Q

Cnidarian taxonomy

A

-subphylum anthozoa
- medusozoa
- myxozoa

38
Q

Phylum Cnidaria

A
  • Radial symmetry (oral-aboral axis)
  • Dipoblastic animals
  • Unique stinging or adhesive structures called cnidae
  • Musculature formed by myoepithelial cells (derived from endo and ectoderm)
  • Diphasic life cycle
  • Coelenteron is the only body cavity
  • No head or discrete gas exchange, excertory or circulatory features
  • Nervous system consists of nerve nets with largely non-polar neurons
39
Q

Dipoblastic

A

Ectoderm and endoderm separated by a cellular mesoglea or partly cellular

40
Q

cnidae

A

unique stinging or adhesive structure. Each cnida resides in is produced by one cell, the cnidocyte

41
Q

Diphasic life cycle

A

Consists of asexual polyploid and sexual medusoid generations but some variations exist on this theme

42
Q

Coelenteron

A

The endodermally-derived gastrovascular cavity. A blind gut with a single opening

43
Q

Phylum Cnideria continued

A
  • 10,000 species mostly marine, some freshwater
  • range in size
  • sessile (polyps) or planktonic (medusae)
  • Sexual reproduction includes a planula larva
  • typically carnivorous though some employ suspension feeding
  • many species harbor symbiotic intracellular photosynthetic dinoflaggelates (zooxanthellae)
44
Q

zooxanthellae

A

photosynthetic dinoflagellates that may harbor symbiosis with some cnidaria

45
Q

Cnidarian bauplan

A

-gastrovascular cavity is partially divided into sections by thin vertical walls of tissue called septa
- some septa bear thickened filaments
- septal filaments extend below partial septa as threadlike acontia which bear nematocysts to subdue prey
- Endoderm and exoderm are separated by a primarily ectodermally derived cellular mesoglea

46
Q

septa

A

thin vertical walls of tissue that divide the gastrovascular cavity

47
Q

Synapomorphy of Cnideria

A

Cnidocytes
- stinging or adhesive structures called cnidae

48
Q

Cniderian support structures

A
  • axial skeletons of protein complexes
  • calcareous sclerites
  • massive calcareous skeletons
  • exoskeletons of chitin and protein
49
Q

Cnidarian nervous system

A
  • simple nerve nets coordinate movements
  • complex sensory organs with statoliths and eyes with lenses
50
Q

lineages of cniderians that have lost a nervous system

A

Myxozoans- parasitic cniderians

51
Q

Myxozoans

A

-Parasitic cniderians that have lost a nervous system
-life cycle involves two hosts: one vertebrate and one invertebrate

52
Q

Phylum Ctenophora

A

-Dipoblastic animals with endoderm and ectoderm separated
- biradial symmetry
- adhesive exocytotic cells called colloblasts
- Gastrovascular cavity with complex branching throughout the body; two small reduced anal pores
- nerve net, apical sense organ
- musculature formed from true mesenchymal cells
-no alteration of generations or polyploid phase
- eight rows of ciliary plates controlled by apical sense organ
- some adults with one long pair of tentacles
- most hermaphroditic with cydippid larva

53
Q

Colloblasts

A

adhesive exocytotic cells
-synapomorphy of Ctenophora

54
Q

Ctenophore nervous system

A
  • Apical sense organ consists of an encased statolith
  • nonpolar neurons form comeplex meshes beneath the comb rows (no axons or dendrites)

ZOOLOGY 300 (5 decks)

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